Arsenal and Chelsea make it to the Europa League last four

A magnificent Alexandre Lacazette free kick sent Arsenal into the Europa League semi-finals 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 semi-finals for the second season in a row with a 3-0 aggregate win.

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.

Chelsea reached the Europa League semi-finals by beating Slavia Prague 4-3 in a roller-coaster game on Thursday, helped by a Pedro brace in a first-half onslaught before withstanding a comeback bid by the Czechs after the break.

Chelsea, who will face Eintracht Frankfurt in the last four, were cruising 4-1 at halftime but Slavia's Petr Sevcik slammed home two strikes early in the second half, narrowing the aggregate score to 5-3.

With the Stamford Bridge crowd increasingly unsettled, and Slavia being roared on by their travelling fans, Sevcik spurned a chance to cut the deficit further.

But Chelsea, having won the first leg 1-0, held on to set up a semi against Eintracht, who beat visiting Benfica 2-0 to go through on away goals after a 4-4 aggregate scoreline.

A Chelsea triumph in the Europa League, a trophy they won in 2013, would secure a way back into the prestigious Champions League if they finish outside Premier League top four this season. They currently sit fifth in the table.

Sarri, who has never won a major final as a coach, said he was determined to see his side triumph this time.