(CNN) -- Arsenal failed to seal third place in the English Premier League after losing 2-1 to Blackburn Rovers at Ewood Park on Monday.
Arsene Wenger's men needed to win to give themselves an unassailable lead over north London rivals Tottenham Hotspur and direct qualification for the Champions League group stage next season.
But Tottenham can now move to only two points behind if they win at Manchester City on Wednesday.
It would then mean Spurs could snatch third place should they win and Arsenal lose in the final round of matches.
It looked an unlikely scenario after Robin van Persie put Arsenal ahead in the first half, but David Dunn equalized for Sam Allardyce's men before Christopher Samba headed the winner.
The win lifts in-form Blackburn over Fulham, Sunderland and Stoke and into 10th in the table, having been worried about relegation in the early part of the season.
Dutch striker van Persie put Arsenal ahead in the 13th minute with his first goal since returning from a five-month layoff.
Midfielder Dunn leveled just before halftime as the Gunners failed to clear a corner from Rovers.
Congolese central defender Samba grabbed the winner with a 68th-minute header, again from a corner.
Arsenal goalkeeper Lukasz Fabianski looked at fault for both goals as he failed to take command of the situation, but was defended, not for the first time this season, by Wenger.
"Their (Blackburn's) main purpose every time is to stop the goalkeeper, not go for the ball, and both times for both goals that happened, " he told ESPN.
"I think he (Fabianski) had no chance as a goalkeeper, he was pushed every time."
In Monday's other game, Hull City's relegation from the Premier League was officially confirmed as they were held to a 2-2 draw at Wigan.
Home defender Steve Gohouri scored the crucial last-ditch equalizer that ended even Hull's mathematical chance of staying up.
They join Burnley and Portsmouth in the second-flight next year.
Wigan's 19-year-old striker Victor Moses scored his first goal for the club to put them ahead before Hull debutant Will Atkinson equalized in the 42nd minute with a header.
Visiting striker Mark Cullen headed Hull in front before the late equalizer with a spectacular overhead kick by the Ivory Coast player Gohouri.