The Blues came into the contest with the best defensive record in the competition, though last weekend were beset by too many missed tackles. They were far from perfect in that regard at Allianz Stadium but were defensively sound where it mattered most, successfully protecting their line until the final moments.
The Waratahs lacked imagination in attack and showed why they have scored the fewest tries in Super Rugby, compounding that problem with disciplinary issues that mounted throughout the game.
Whenever the hosts were able to build pressure, particularly in the opening quarter, a penalty would release the valve, while the Blues were also repeatedly pinged in a first half dominated by stoppages.
A frustrating spell for the visitors ended with a lead, however, as Ofa Tuʻungafasi finished what he had started with a scrum penalty to forge the opportunity. The All Blacks prop propelled a dominant set piece throughout his 45 minutes, boosting a side whose talent-laden backline experienced a quiet night.
Stephen Perofeta stood out for the wrong reasons, missing four shots at goal as the Waratahs at one stage conceded seven straight penalties. With the No 10 also overcooking a kick for the corner, his miscues were threatening to prove costly.
But the Blues extended their advantage as a strong carry from Hoskins Sotutu opened space for Zarn Sullivan to waltz over the line, creating enough breathing room to withstand a late try for Jay Fonokalafi.
Blues 12 (Ofa Tuʻungafasi, Zarn Sullivan tries; Stephen Perofeta con, pen)
Waratahs 10 (Jay Fonokalafi try; Tane Edmed pen, con)
HT: 7-3
