Considering the few fouls that were committed in the first half and the two mistakes Dereli made (missed a hands ball, missed a foul), you could say he was 20% wrong. Not a good record.
But in the second half he showed himself to be not a bad a referee at all. He booked only twice (one for a foul and one for stalling for time) and was lenient. He always looked for a chance to give the advantage after a foul and let the game go on whenever that was possible. Again there were little mistakes - a throw in for the wrong team, things like that - but they were of no consequence.
AZ had two matches to lose: the one for a place in the next round of the UEFA Cup and the one leading to some sort of a record. AZ had never lost a home match in an international tournament. Never ever since they were formed in 1967. Tonight they lost both matches.