Portsmouth climbed to second in the Premiership with a magnificent victory over Middlesbrough at The Riverside.
Matthew Taylor (left) celebrates with Kanu after Pompey's opener
Kanu's brace brought the hosts crashing back to earth after their win over Chelsea, the striker poking home from close-range to put Pompey in front.
Boro's Yakubu was twice foiled by David James before Benjani Mwaruwari was left unmarked to head in from a corner.
Kanu made it 3-0 with a fabulous solo effort and substitute Svetoslav Todorov chipped in a fourth in stoppage time.
Boro have not beaten Portsmouth in the league since 3 December 1994 and they never looked like ending that dismal run on Teesside.
Harry Redknapp's Pompey started like an express train and they never gave Boro a chance to get a grip on proceedings.
The game was only five minutes old when Mark Schwarzer was forced to sprawl across his line to claw behind a goal-bound 25-yard free-kick from Dejan Stefanovic.
And Pompey made Boro pay for their early inertia when the resulting corner was not cleared and Kanu pounced to prod in his third goal of the season.
The hosts seemed incapable of ever clearing their lines and they were let off moments later when David Thompson sliced wide after yet more hesitant defending.
Pompey looked full of confidence and Stefanovic was marauding down the left at every opportunity to cause Boro problems.
Gareth Southgate's side slowly improved and Yakubu went close twice, first having a header saved by James then shooting at the keeper from 22 yards.
Lee Cattermole and Gaizka Mendieta curled wide too before Kanu nearly doubled the visitors' lead, his stinging drive parried away by Schwarzer.
Boro wanted a goal at the start of the second half and Mark Viduka headed over and Yakubu blazed wide as they began promisingly.
But Southgate's team-talk was soon left in tatters as more sloppy marking left Mwaruwari free at the back post to nod in David Thompson's right-wing corner.
Boro desperately tried to find a way through and three times they came close to halving the deficit.
Svetoslav Todorov lifts the fourth over the advancing Mark Schwarzer
Mendieta volleyed just over, James brilliantly tipped over Stewart Downing's free-kick and then Chris Riggott's header was scooped off the line by Gary O'Neil.
Just as the Riverside crowd were beginning to think their team could get back into the game, Kanu scored a majestic third to stun the home faithful.
With Boro pressing he ran from inside his own half, holding off the challenge of George Boateng, to impudently chip over the advancing Schwarzer and into the net.
Southgate made a triple substitution with 20 minutes to go but by then the game was over, the imperious Sol Campbell ensuring Boro had no way back in.
Sub Todorov secured Pompey's biggest ever Premiership away win in injury time when he latched onto Sean Davis' pass and lobbed over Schwarzer.
Middlesbrough boss Gareth Southgate:
"We still have plenty we need to work on.
"Everyone knows they did not produce but I take responsibility and we'll dust ourselves down and start again.
"Let's give Portsmouth credit because they look a good side. We didn't hit the heights of the other night against Chelsea and we will look at why. We must improve."
Portsmouth manager Harry Redknapp:
"Kanu was sitting around all summer and no one else wanted him - anybody could have had him, he was just waiting and he has been fantastic.
"It was a good performance, we did ever so well, but I do worry if we get injuries we'll be bang in trouble.
"Linvoy Primus, Sol Campbell and David James did really well. Sol's a rock."
Middlesbrough: Schwarzer, Parnaby, Riggott, Pogatetz, Taylor, Mendieta (Rochemback 70), Cattermole (Morrison 70), Boateng, Downing, Viduka (Christie 70), Yakubu.
Subs Not Used: Turnbull, Davies.
Booked: Parnaby, Downing.
Portsmouth: James, Pamarot, Primus, Campbell, Stefanovic, O'Neil, Davis, Thompson (Koroman 73), Taylor (Hughes 86), Kanu (Todorov 83), Mwaruwari.
Subs Not Used: Jordan, O'Brien.
Goals: Kanu 7, Mwaruwari 50, Kanu 57, Todorov 90.
Ref: C Foy (Merseyside).