Geoff Horsfield's two goals gave West Brom the spoils at The Hawthorns and left Portsmouth pointless at the foot of the Premiership table.
Horsfield caught Pompey napping when he climbed at the far post to head the Baggies in front after two minutes.
He doubled Albion's lead after the break when Pompey keeper Sander Westerveld allowed his shot to squirm under him at the near post.
Laurent Robert gave Pompey hope with an exquisitely-struck free-kick.
Albion were out of the blocks fast while Portsmouth were still napping, taking the lead after just two minutes.
Jonathan Greening swung in a cross from the left and Horsfield stole in between two Pompey defenders to power his header downwards and over Westerveld's dive.
Portsmouth looked disjointed and surrendered possession too cheaply in midfield, while they continued to be sloppy at the back early on.
Pompey had a sight of goal when Lomano Lua Lua latched on to Robert's pass but the Congo international's first touch was too heavy.
Although he was clipped by Thomas Gaardsoe, referee Mike Riley ruled Lua Lua had lost control of the ball.
Robert's free-kick gave Pompey hope
Despite Portsmouth getting more of a handle on the game, a quick Albion break saw Horsfield connect with Zoltan Gera's cross, only to fire over from 10 yards.
Lua Lua was largely forced to forage on his own up front and when he fired the ball across the face of goal there was no red shirt to apply a finishing touch.
In contrast, Albion's midfielders were given licence to push on and Andy Johnson fired inches wide after good hold-up play from Kevin Campbell.
The skills of Greening and Lua Lua briefly illuminated an afternoon of industry and application more suited to the midfield scurryings of Ronnie Wallwork and Richard Hughes.
The game was drifting through a scrappy, aimless phase when a howler from Pompey keeper Westerveld gifted Albion a second goal.
Horsfield cut in from the right and his half-hit shot squirmed under Westerveld at the near post and, although Campbell followed up to make sure, the goal was credited to Horsfield.
Robert, who had wasted two previous dead-ball opportunities, brought Pompey back into the game almost immediately by curling in a free-kick from 20 yards.
Svetoslav Todorov and Vincent Pericard were introduced after long absences, but Pompey still lacked any sort of cutting edge to break Albion down.
And in the dying minutes, it was Giannis Skopelitis who blasted over from five yards out.
West Brom assistant manager Nigel Pearson:
"We could have made it more comfortable for ourselves.
"We gave away some silly free-kicks and created most of our problems ourselves because you can only give Laurent Robert so many chances.
"But there were more plusses than minuses from the game and it's good to get that first win under our belts."
Portsmouth manager Alain Perrin:
"For their second goal I was more concerned with how we lost the ball in the middle than Sander's error.
"It was always difficult for us after we lost the first goal so early on and although we weren't very good in the first half, we improved in the second.
"We had chances to score and in the end we were unlucky not to get a draw."
West Brom: Kirkland, Watson (Earnshaw 83), Gaardsoe, Robinson, Clement, Gera (Albrechtsen 66), Johnson, Wallwork, Greening, Horsfield, Campbell.
Subs Not Used: Kamara, Ellington, Kuszczak.
Booked: Campbell, Gera, Johnson, Horsfield.
Goals: Horsfield 2, 59.
Portsmouth: Westerveld, Griffin (Skopelitis 84), O'Brien, Stefanovic, Vignal, O'Neil (Todorov 70), Viafara, Hughes, Robert, LuaLua, Karadas (Pericard 81).
Subs Not Used: Ashdown, Taylor.
Booked: Viafara, Karadas, Vignal.
Goals: Robert 63.
Referee: M Riley (W Yorkshire).