Arsenal were very quick to take the lead (after less than 75" from kick-off) and haven't let off since. It was a good game of football and the ref adapted well to the quality of it.
Kassai and his ars
Viktor Kassai was one of the beaming lights among referees at WC 2010. Then there was the atrocious performance at Euro 2012 (England-Ukraine), more let down by his ar and aar (Eros and Vad, respectively) than his own fault. However, this incident defined his refereeing for the next two seasons, which has been under par and cost him to be dropped from the final list of referees for WC 2014. Hopefully, the Arsenal-Dortmund encounter is a sign of him to recover and reassert his refereeing authority. The old positive finger-tips of letting the game flow were there, however with some old negative flaws of not detecting some fouls in mid-field. There was one important improvement as he brandished the yellow card twice in the first 15 minutes, stamping his authority (in the past he sometimes delayed such an act for too long, thus causing players to misunderstand and deteriorate into brutality). His ars, Ring and Toth, typically of Hungarian ars, were much less convincing than the man in the middle.