* Juventus snatch late winner against Lyon
* Porto and Benfica both win first legs 1-0
* Basel comfortably defeat Valencia 3-0 (Adds details, quotes)
By Toby Davis
LONDON, April 3 (Reuters) - Juventus left it late before putting a foot in the Europa League semi-finals on Thursday, edging a stubborn Olympique Lyon 1-0 with a goal from Leonardo Bonucci as Basel, Porto and Benfica also grabbed first-leg wins.
Swiss side Basel took a huge step towards a second successive last-four appearance as Matias Delgado scored twice and Valentin Stocker netted a third in injury time in a 3-0 win over Valencia played behind closed doors.
Porto and Benfica made it a good night for the Portuguese with 1-0 wins over Sevilla and AZ Alkmaar respectively ahead of next week's return legs.
Eliaquim Mangala scored with a header in the 31st minute for Porto, who finished with 10 men, at home to Spanish side Sevilla while Eduardo Salvio volleyed home three minutes after halftime to give Benfica victory in the Netherlands.
Lyon coach Remi Garde said ahead of the quarter-final tie that his injury-hit side had a mountain to climb if they wanted to get past Serie A champions and triple winners Juventus.
For 85 minutes, however, the two teams went toe-to-toe in an edgy encounter where chances were at a premium and the fear of defeat seemed to trump any desire to cast off the shackles.
The best chance of a cagey first half fell to Serie A top scorer Carlos Tevez after six minutes but he headed wide to extend a European goal drought that stretches back to April 2009.
Lyon's best two opportunities arrived in the first half when Steed Malbranque forced a good save from Gianluigi Buffon and Jimmy Briand lifted a good chance over from close range.
Juventus, eight points clear at the top of Serie A, showed their quality in restricting the hosts to minimal sights of goal and then snatching a late victory that puts them in the box seat ahead of the return leg in Turin.
The French side failed to clear a cross from the left and the ball landed at the feet of Bonucci who was left with a simple finish.
"In the first half we struggled to find enough spaces to play our football while after the break we didn't risk anything other than on set pieces," Bonucci told Mediaset.
"Lyon ran very hard in the first half but in the second we were able to bring home a very important victory."
Basel's clash with Valencia was played behind closed doors after fan trouble in the Swiss team's last-16 tie in Salzburg but the muted atmosphere did little to hamper the hosts who took the lead after 34 minutes, Delgado finding the net with a precise finish from the edge of the area.
That was the first goal Valencia had conceded in 400 minutes of Europa League action but their back line was breached for a second time four minutes later when the same player finished from close range.
Stocker gave Basel a comfortable lead to defend in the tie when he lifted the ball over Valencia keeper Vicente Guaita in stoppage time.
Porto went into the game against Sevilla having won their last three matches at home including a 1-0 victory over Napoli in the last 16.
They took the lead after 31 minutes when Mangala headed home emphatically from Ricardo Quaresma's superb cross from the left.
Sevilla came back into the match in the second half and Carlos Bacca tested the Porto keeper with a low strike while substitute Kevin Gameiro should have put the rebound in but skewed his shot wide.
The game ended on a sour note for the hosts when midfielder Fernando was sent off for his second booking with four minutes remaining.
Alkmaar were the only quarter-finalists who remained unbeaten from the group stage this season and would have taken the lead against last season's runners-up Benfica were it not for two good stops from Artur.
The visiting keeper saved with his legs to deny Aron Johannsson and then acrobatically kept out a swerving effort from Steven Berghuis in the first half.
The Dutch side fell behind three minutes after the restart when Salvio showed excellent technique to control a volley after some comically bad defending by the home team resulted in AZ keeper Esteban saving from Oscar Cardozo. (Editing by Tony Jimenez)