Arsenal manager Arsene Wenger was left frustrated by Swansea's style of play after Garry Monk's side completed a shock 1-0 win to dent the Gunners' hopes of finishing second in the Premier League.
The Gunners dominated the game at the Emirates Stadium and created a number of excellent chances in the second half but it was the visitors who grabbed a late winner after Bafetimbi Gomis' 85th-minute header was ruled to have crossed the line by the goal-decision system.
It was one of only three efforts on target from the visitors on the night, in comparison to Arsenal's nine, and Wenger was frustrated by his opponents' defensive approach.
"We were unlucky I think against a team who refused to play completely and just defended," Wenger said. "We've scored plenty of goals until recently.
"In the last two home games we didn't score and that was frustrating when you have so much of the ball and play with such accuracy around the box.
"They defended well. They came just to defend with four defenders and six midfielders, and they defended. That's it.
"If you win, you're fantastic but if you lose people say to you, 'Why did you not play?' They won so they are fantastic."
Olivier Giroud, Theo Walcott and Aaron Ramsey all squandered opportunities to put Arsenal in front while Alexis Sanchez had the best chance of the game at 0-0, but could only find Lukasz Fabianski from seven yards out.
"We rushed our finishing," Wenger said. "Sometimes we were maybe too eager to finish alone rather than passing the ball.
"Sometimes we had to force the situation and in the end you have to give them credit -- they defended well."
The defeat means Arsenal miss the chance to move level on points with Manchester City in second.
Wenger's side still have a game in hand over both City, who they trail by three points, and Manchester United, who they lead by two and face at Old Trafford on Sunday.
"It's very important to finish in the top three," Wenger added. "We still have a game in hand. What is crucial is to respond on Sunday and show that it was an accident today. That is the most important thing."