League One Brentford served up the night's big upset and triggered scenes of jubilation in West London by knocking out Premier League Everton 4-3 on penalties after holding the visitors 1-1 in normal time.
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With the score also 1-1 after the 90 minutes at White Hart Lane, French midfielder Nasri overcame his own superstition to shatter Spurs' hopes with two spot kicks in the space of three minutes early in extra-time.
"He had a superstition to think that when the penalty is made on you, not to take it," said Arsenal manager Arsene Wenger after his club's biggest win at White Hart Lane in 32 years.
"I tried to prove to him that it's only based on fear. It's gone tonight... he realises now it was a bad superstition."
The first penalty was awarded after Nasri was tugged by Sebastien Bassong and the second when Steven Caulker fouled Marouane Chamakh.
Second-half substitute Andrey Arshavin delivered the final blow with a low shot from the edge of the box.
"I thought the first one (penalty) was harsh," said Tottenham manager Harry Redknapp. "Really, I think he's dived. The second one was a blatant penalty."
OTHER UPSET
Second division Burnley savoured the night's other upset with a 1-0 home win over their former manager Owen Coyle's Premier League Bolton Wanderers.
Struggling West Ham United won 2-1 at Premier League rivals Sunderland and, in another all top-flight clash, Stoke City beat Fulham 2-0, while Birmingham City saw off third division Milton Keynes Dons 3-1.
Arsenal were by far the better team in the first half against Spurs and went ahead in the 15th minute with England under-21 international Henri Lansbury scoring his first senior goal for the club.
The arrival of Robbie Keane after the break revived Spurs and the Irishman equalised just three minutes into the second half with a shot that rolled into the net despite goalkeeper Lukasz Fabianski getting his hands to the ball.
Keane could have wrapped it up for the hosts in the 83rd when he smacked a shot against the left upright.
The match started after a minute's applause for former England international Bobby Smith, centre-forward in Tottenham's double-winning side of 1960/61, who died on Saturday aged 77.
Wenger, serving a one-match touchline ban for his behaviour at Sunderland on Saturday, watched from the directors' box and had to resort to texting instructions to the dugout.
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