As for the pressure he has been under after saying goodbye to Marshall and his failed switch from league, Kirwan, who clearly wasn't getting carried away with this victory, said it was par for the course.
"That was my main focus, to handle the stuff off the field and make sure we prepared properly. The pressure is going to come on again and there will be other times when it's not there, but that's what we do and if you don't like that you shouldn't be in this industry, really."
Ma'a Nonu, who missed the Hurricanes defeat with a calf problem, was direct and aggressive and Jerome Kaino put in one of his most influential performances of the season.
Try scorers Francis Saili and Lolagi Visinia were dangerous and in Frank Halai and Charles Piutau they had able assistants.
Piri Weepu, back from his health scare, played most of the second half off the reserves bench.
The four competition points keep the Blues in touch with the other New Zealand teams and edge them up the table to eighth. More than that, it allows them to recalibrate after the Marshall mess. They will look forward to the Reds at Eden Park next Friday with renewed confidence.
The Waratahs would have left the field at halftime wondering how they weren't in the lead. With men like Kurtley Beale and Israel Folau in their side they had every right to look for an expansive game, but their ambition was their undoing at times. Final passes went to ground when players were in scoring opportunities, literally in the case of Bernard Foley, who had done so well to break through only to throw a shocking pass to unmarked wing Cam Crawford.
Coach Michael Cheika was seething afterwards.
"Tonight we set ourselves an objective to play attacking rugby. To do that you've got to have good skills but we threw the ball away like it was a piece of dirt. We didn't respect it and we basically handed the opposition the match."
Visinia's try owed much to the directness of Nonu, who burst through the defence and featured later when throwing the long cut-out pass for Visinia, and Saili capitalised on quick thinking from his teammates following a botched Bernard Foley kick.
They had a bit of luck - Rob Horne's effort in the second minute was ruled out for a double movement and he knocked on with a clear run to the line later in the half.
Folau, the Waratahs' main attacking threat this season, couldn't get going, with Nonu in particular testing his positional play with grubber kicks. A tactical win to go with their physical dominance. A precious victory indeed.
Blues 21 (Lolagi Visinia, Francis Saili tries; Simon Hickey 3 pens, con)
Waratahs 13 (Jacques Potgieter try; Bernard Foley 2 pens, con)
HT: 8-3
