Jerome Thomas was sent off for a shove on Jack Wilshere
Sanchez Watt scored his first senior goal as an Arsenal side featuring eight teenagers saw off 10-man West Brom.
The Baggies' hopes suffered a blow when ex-Gunners trainee Jerome Thomas was sent off after 37 minutes for a clash with Jack Wilshere.
Arsenal needed 68 minutes to open the scoring, Watt pouncing after substitute Carlos Vela's shot was saved.
Vela then took advantage of a mistake by Leon Barnett to tap in after Mark Randall's chip came off the bar.
As expected, Arsene Wenger stuck to his policy of blooding his young players in the Carling Cup, with the likes of keeper Wojciech Szczesny and forwards Watt and Gilles Sunu getting their chance to shine.
Philippe Senderos and Mikael Silvestre added experience at the back, and took the average age of the team to just over 20, but it was the Baggies who had the better of the first half.
Wenger impressed with 'solid' Gunners
Simon Cox and Rob Koren forced good saves from Szczesny, while Kerrea Gilbert and Kieran Gibbs cleared off the line for the Gunners, but Thomas's petulance cost the visitors.
The 26-year-old was shown a straight red card when he shoved Wilshere to the floor as the pair clashed following the Arsenal midfielder's challenge.
But the Gunners continued to toil until Wenger introduced Mexican star Vela just before the hour mark.
The 20-year-old, who missed the start of the season with an ankle injury, created space for a shot which Dean Kiely could only palm into the path of Watt, who showed great poise to slot in the opener.
Vela made the game safe after 75 minutes - albeit with some help from Baggies defender Barnett.
After Randall's 20-yard chip came back off the bar, Barnett tried to chest the ball back to Kiely only for Vela to steal in.
Arsenal boss Arsene Wenger: "When Vela came on, straight away he made a difference.
"He is dangerous in his control, movement and class. He gives you something special.
"He still has work to do on his fitness, but he is in my plans."
West Brom boss Roberto di Matteo on the sending off: "Thomas went to shake hands with Wilshere, he refused and Thomas reacted. I am disappointed Wilshere did not accept his hand.
"That was the turning point. I felt before Thomas got sent off, we were starting to get on top of them."
90:00+4:17 The referee signals the end of the game.
90:00+4:04 Nacer Barazite has an effort at goal from just outside the box which goes wide of the right-hand upright.
90:00+3:30 Mark Randall gives away a free kick for an unfair challenge on Youssouf Mulumbu. Free kick taken by Youssouf Mulumbu.
90:00+2:27 Free kick awarded for an unfair challenge on Graham Dorrans by Mark Randall. Direct free kick taken by Dean Kiely.
90:00+0:06 Kerrea Gilbert takes a shot. Dean Kiely makes a save. Corner taken by Jack Wilshere from the right by-line to the near post.
87:03 Robert Koren crosses the ball, save by Wojciech Szczesny.
86:39 Foul by Gianni Zuiverloon on Nacer Barazite, free kick awarded. Nacer Barazite takes the free kick.
83:13 Foul by Jack Wilshere on Robert Koren, free kick awarded. Gianni Zuiverloon restarts play with the free kick.
82:18 The ball is crossed by Nacer Barazite, clearance by Gonzalo Jara.
80:09 Carlos Alberto Vela gives away a free kick for an unfair challenge on Gianni Zuiverloon. Direct free kick taken by Dean Kiely.
79:28 Substitution Jonas Olsson leaves the field to be replaced by Abdoulaye Meite.
79:16 Shot by Chris Wood from deep inside the penalty area misses to the right of the goal.
77:49 Free kick awarded for an unfair challenge on Filipe Teixeira by Mark Randall. Free kick taken by Graham Dorrans.
77:23 Foul by Sanchez Watt on Gianni Zuiverloon, free kick awarded. Free kick taken by Gianni Zuiverloon.
76:25 Jack Wilshere gives away a free kick for an unfair challenge on Jonas Olsson. Direct free kick taken by Dean Kiely.
75:25 GOAL - Carlos Alberto Vela:Arsenal 2 - 0 West Brom Carlos Alberto Vela grabs a goal from close in to the top left corner of the goal. Arsenal 2-0 West Brom.
74:55 Mark Randall has an effort at goal from 25 yards.
74:29 A cross is delivered by Nacer Barazite.
73:36 Substitution Chris Wood replaces Luke Moore.
72:53 Luke Moore takes a shot. Save by Dean Kiely.
71:37 Aaron Ramsey takes a shot. Save made by Dean Kiely.
70:56 Free kick awarded for an unfair challenge on Carlos Alberto Vela by Leon Barnett. Direct free kick taken by Nacer Barazite.
69:22 A cross is delivered by Carlos Alberto Vela, Gianni Zuiverloon gets a block in. Short corner taken by Jack Wilshere.
68:10 Substitution Nacer Barazite comes on in place of Armand Traore.
67:41 GOAL - Sanchez Watt:Arsenal 1 - 0 West Brom Goal scored by Sanchez Watt from inside the six-yard box to the bottom left corner of the goal. Arsenal 1-0 West Brom.
67:19 Carlos Alberto Vela takes a shot. Save by Dean Kiely.
65:38 The ball is sent over by Gianni Zuiverloon, Philippe Senderos makes a clearance.
63:28 The ball is delivered by Armand Traore, clearance made by Gonzalo Jara.
62:02 Sanchez Watt challenges Leon Barnett unfairly and gives away a free kick. Dean Kiely restarts play with the free kick.
60:21 Free kick taken by Dean Kiely.
60:21 Substitution Youssouf Mulumbu replaces Simon Cox.
60:21 Filipe Teixeira fouled by Jack Wilshere, the ref awards a free kick.
59:09 Simon Cox takes a shot. Save made by Wojciech Szczesny.
57:17 Substitution Carlos Alberto Vela joins the action as a substitute, replacing Gilles Sunu.
57:17 Substitution Mark Randall replaces Francis Coquelin.
57:17 The ball is delivered by Gianni Zuiverloon, Simon Cox has a headed effort from close range and clears the bar.
56:27 Dean Kiely takes the direct free kick.
56:27 Booking Aaron Ramsey shown a yellow card.
55:09 Gonzalo Jara concedes a free kick for a foul on Aaron Ramsey. Jack Wilshere delivers the ball from the free kick left-footed
from left channel, Luke Moore makes a clearance. Free kick awarded for a foul by Aaron Ramsey on Leon Barnett.
50:10 Filipe Teixeira challenges Kerrea Gilbert unfairly and gives away a free kick. Wojciech Szczesny takes the direct free kick.
48:24 Free kick awarded for an unfair challenge on Filipe Teixeira by Kerrea Gilbert. Gonzalo Jara takes the free kick.
45:01 The referee gets the second half underway.
45:00+2:17 The match has reached half-time.
45:00+1:31 Centre by Armand Traore, clearance made by Robert Koren.
44:17 Free kick awarded for an unfair challenge on Jack Wilshere by Luke Moore. Aaron Ramsey has an effort direct from the free
43:41 Simon Cox is ruled offside. Mikael Silvestre restarts play with the free kick.
42:48 Mikael Silvestre concedes a free kick for a foul on Simon Cox. Graham Dorrans takes the free kick.
41:13 The referee blows for offside. Dean Kiely takes the free kick.
40:18 Free kick awarded for an unfair challenge on Aaron Ramsey by Simon Cox. Aaron Ramsey takes the direct free kick.
37:56 Philippe Senderos restarts play with the free kick.
37:25 Booking Simon Cox booked.
36:48 Sent off Jerome Thomas is shown a red card.
35:59 Jerome Thomas sends in a cross, save by Wojciech Szczesny.
35:23 Kerrea Gilbert challenges Jerome Thomas unfairly and gives away a free kick. Gonzalo Jara restarts play with the free kick.
34:06 Free kick awarded for an unfair challenge on Jack Wilshere by Simon Cox. The free kick is swung in right-footed by Aaron Ramsey,
clearance by Luke Moore.
31:11 Free kick crossed by Graham Dorrans.
31:11 Booking Philippe Senderos receives a yellow card.
31:08 Philippe Senderos challenges Simon Cox unfairly and gives away a free kick.
30:14 Jack Wilshere produces a left-footed shot from outside the penalty box and misses right.
28:15 Simon Cox sends in a cross.
26:38 Simon Cox is ruled offside. Free kick taken by Mikael Silvestre.
Correction - 23:03 Armand Traore concedes a free kick for a foul on Filipe Teixeira. Dean Kiely takes the direct free kick.
23:03 Armand Traore concedes a free kick for a foul on Filipe Teixeira. Free kick taken by Jonas Olsson.
22:25 The ball is swung over by Gilles Sunu, Leon Barnett manages to make a clearance.
22:21 Sanchez Watt sends in a cross, Leon Barnett makes a clearance.
21:58 Kerrea Gilbert produces a cross, Jonas Olsson makes a clearance.
21:39 Free kick awarded for an unfair challenge on Jack Wilshere by Robert Koren. Direct free kick taken by Kerrea Gilbert.
20:36 Filipe Teixeira sends in a cross, Philippe Senderos manages to make a clearance.
18:55 Robert Koren has a drilled shot. Save made by Wojciech Szczesny. Inswinging corner taken right-footed by Robert Koren, Francis
Coquelin makes a clearance.
17:54 Effort from the edge of the box by Simon Cox goes wide of the left-hand upright.
17:07 Shot by Sanchez Watt from deep inside the box hits the post.
15:46 Effort from the edge of the area by Robert Koren goes wide of the right-hand upright.
13:00 Inswinging corner taken left-footed by Jack Wilshere from the right by-line, save made by Dean Kiely.
8:49 The assistant referee flags for offside against Luke Moore. Philippe Senderos takes the free kick.
7:56 Gianni Zuiverloon crosses the ball, Kieran Gibbs gets a block in. Corner taken right-footed by Graham Dorrans, Wojciech Szczesny
manages to make a clearance.
6:01 Aaron Ramsey sends in a cross.
3:39 Corner taken by Jack Wilshere played to the near post, Close range header by Philippe Senderos misses to the right of the
2:13 Outswinging corner taken from the left by-line by Jack Wilshere, Philippe Senderos produces a header from inside the six-yard
box that clears the bar.
2:07 Kieran Gibbs sends in a cross, Leon Barnett gets a block in.
0:00 The match has kicked off.
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