Sportal.co.nz 11.Mar.2013Getty Images
Kirwan's youthful squad failed to execute the expansive style of play that saw them upset the Hurricanes and Crusaders in previous weeks and were outscored three-tries-to-two.
Facing the Bulls, known for their strong kick-chase game and bruising forward play, Kirwan said his troops strayed from the patterns they practised and instead played a style that accommodated their opposition.
The loss, their first of the season, was described by the new coach as the 'worst performance' he has witnessed so far.
"I didn't think we performed to be honest," Kirwan said after the game.
"I felt that we didn't play what we trained all week so that was disappointing.
"It was pretty poor really."
Captain Ali Williams was irate after the Bulls were allowed to triumph at Eden Park for the first time in 16 years and hinted that complacency may have been an issue for some players.
"We're a team that plays with the ball and stresses defences and we resorted to playing their style of football, which, they are the best in the world at," said Williams.
"There was no spark. That can't come from a coaching staff, that comes from within, individually, and then it comes collectively by looking at your mates and saying 'here's another chance to wear the Blues jersey'.
"I'm pretty pissed off at how we played, purely because of our attitude towards playing Blues rugby."
Six debutants were thrown in the deep end against the three-times Investec Super Rugby champions; a decision that Kirwan admits did cost them.
Taranaki wing Waisake Naholo epitomised the difference in class between personnel on either side and made a number of costly errors - one led to the Bulls' second try.
Rookie first-five Baden Kerr will also rue his botched kick in midfield that also contributed to that same five-pointer.
He must also take responsibility for not commanding the game plan. However, Kirwan felt any type of critism should land squarely on him.
"We made some changes and I think we trained probably not as well as we could have all week," Kirwan added.
"I'll cop that on the chin and we just need to get back into it."
Meanwhile, Bulls coach Frans Ludeke was pleased with the way his side achieved its goals, which included shutting down the Blues' ability to offload in contact.
"Obviously any win away, especially in New Zealand, is special, it doesn't come easy," Ludeke said.
"We had to put together a special effort to accomplish that.
"I must say it's really satisfying."
The Bulls scored all three of their tries through sweeping passing plays, as opposed to the crash and bash style that is their bread and butter.
Captain Pierre Spies highlighted the importance of having alternative options on attack to avoid being too predictable.
"We like to vary our game a bit and make use of opportunities we're given," Spies added.
"You've got to have a complete game to win the competition."
The Blues will use next week's bye to dissect the loss while the Bulls prepare to face the Crusaders in Christchurch.