Madrid, April 14 (IANS): Manchester United, who drew 1-1 away at Anderlecht, and Ajax, 2-0 winners at home over Schalke 04, emerged the strongest in the Europa League quarterfinal first leg.

The outlook is more complicated for Celta Vigo who on Thursday won but conceded two away goals to Genk, while Olympique Lyon prevailed 2-1 against Besiktas in a match that started 50 minutes late due to clashes between home-team supporters and travelling Turkish fans, reports Efe.

Henrikh Mkhitaryan scored in the 37th minute to stake Man United to a 1-0 lead in the match at Constant Vanden Stock Stadium in Belgium.

The visitors preserved their advantage until the 86th minute, when Leander Dendoncker equalised for Anderlecht, but the away goal means United need only a scoreless draw in the second leg at Old Trafford to claim a berth in the semifinals.

Ajax were the most impressive side of the day, dominating Schalke 2-0 at Amsterdam Arena.

Davy Klaassen scored both goals. The first coming in the 23rd minute on a penalty, the second in the 53rd with an assist from Justin Kluivert.

Celta got off to a rocky start at Vigo's Balaidos stadium, conceding at the 10-minute mark to Genk's Jean-Paul Boetius.

The hosts pulled level five minutes later on a goal by Pione Sisto and took a 2-1 lead in the 18th minute courtesy of a strike from Iago Aspas.

The Spanish side looked to be in full command after John Guidetti scored in the 38th minute to make it 3-1.

But Genk got what could turn out to a decisive second away goal thanks to a Celta defensive miscue that set up Thomas Buffel's goal in the 67th minute.

In Lyon, pre-match tensions between Olympique and Besiktas fans spilled onto the pitch, requiring police to intervene.

The delay seemed to have no impact on the Turkish squad, who jumped out to a 1-0 lead with a goal in the 15th minute by Ryan Babel and looked likely to come away with the victory until the final 10 minutes, when Olympique rallied.

Corentin Tolisso brought the hosts level with a goal in the 83rd minute and Jeremy Morel scored the eventual match winner two minutes later. 

Commenting on the match, coach Jose Mourinho said the result was good but they could have been better in the middle.

"The result is positive - to play at home with an advantage, to start the game with an advantage, it is a good result but I think the result should be much better," Mourinho was quoted as saying by the club's official website.

"We can only blame ourselves because we had an easy game to play in the second half and we didn't play in attack with that instinct. We lost the ball easily too many times, we stopped our counter-attacks because of sloppy decisions, sloppy touches of the ball and then we gave them opportunity to have some counter-attacks," he added.