A magnificent Alexandre Lacazette free kick sent Arsenal into the Europa League semifinals with a comfortable 1-0 win away to a toothless Napoli on Thursday, ending Serie A's interest in European competition this season.

The Frenchman struck in the 36th minute to earn Arsenal a tie against Valencia, just as Napoli, trailing 2-0 from the first leg, were threatening to take control of the game.

Carlo Ancelotti's team lost their way after that and, although the hosts had 67 percent of possession, Arsenal were able to sit out the second half to reach the semifinals for the second season in a row with a 3-0 aggregate win.

"We came here with ambition, we wanted to win, to score some goals. We did it, and kept a clean sheet as well, which is important for the confidence," said Arsenal defender Laurent Koscielny.

Ancelotti said that "the game lasted 30 minutes."

"We had two chances to score and we didn't succeed," he added. "We have not been as lucid in the last two months, we are more predictable and because of that, we have difficulty with our finishing."

In a lively opening half hour, Napoli threatened to make a breakthrough as Jose Callejon's effort was saved by Petr Cech's legs and Arkadiusz Milik had a goal chalked off for offside.

The Pole should have put Napoli ahead minutes later when compatriot Piotr Zielinski's cross found him unmarked in the penalty area but he headed wide.

Arsenal also lost Aaron Ramsey to an apparent hamstring problem but, just as it seemed things were going against them, they went ahead as Lacazette curled his free kick around a poorly organised wall from 25 metres.

Arsenal should have wrapped up the game four minutes into the second half but Pierre-Emerick Aubameyang, with only Alex Meret to beat, placed his shot too near the goalkeeper who was able to save.

The second half petered out after that as Arsenal sat back and Napoli enjoyed most of the possession but did little with it.

Lorenzo Insigne shot weakly at Cech after getting clear of the Arsenal defence and was immediately substituted, a decision which infuriated the forward who watched the rest of the match on the touchline with his arms folded.

Fabian Ruiz summed up their evening by firing their last chance wildly over the crossbar in stoppage time.

"Insigne was just disappointed with the way the match went, he had believed in our chances like everyone else," said Ancelotti. "His reaction was not linked to the substitution."