For the most part he was quite good, and let the match flow as much as possible, playing advantage on a number of occasions. Play was only stopped for 23 fouls, quite a few less than most Champions League matches. The assistants got most things spot on.
The second half, which saw Manchester United fighting hard and producing some excellent football on the attack (even if the defence still looked flaky), produced a few problems for the referee. Firstly he ruled that Darren Fletcher was guilty of simulation and booked him. However, instead of reaching for the card, he should have been pointing to the spot since Fletcher had clearly been tripped.
The second half saw seven bookings. Not all of them were necessary, and a diplomatic telling off would have been better in some instances. All those cards made it seem like he was battling to stay in control of the match, whether he was or not. I did agree with both yellow cards that Semberas received.
Benquerenca is clearly not yet at the same level as Busacca, Rosetti, de Bleeckere and Larsen, but he has the potential to be a top Champions League referee in the next few seasons.