They have done it again.
A heroic effort from Leon MacDonald's next generation squad has propelled the Blues to a franchise-record winning mark.
Last week in Canberra the Blues needed Beauden Barrett to nail an injury-time drop goal to snatch victory.
On Saturday night, in front of a packed Leichhardt Oval in Sydney, this time Zarn Sullivan stepped up to nail a clutch, match-winning drop goal to cap a courageous comeback from the vastly understrength Blues.
MacDonald's men don't know how to lose at present. The Blues have now surpassed the 1997-championship winning side to extend their winning run to 13 matches.
Against the Waratahs, a Blues team that featured 14 starting changes survived two first-half yellow cards and overturned a 14-3 second-half deficit through tries to Cameron Suafoa and Luke Romano.
Captaining the Blues for the first time, Romano charged over with blood streaming from his eye, only for Waratahs playmaker Tane Edmed to knock over a penalty and level the contest with one minute remaining.
As they did last week, only this time with a host of fresh faces, the Blues held their composure to calmly work their way down field and put Sullivan in position to ice the left-footed winner as a swarm of Waratahs defenders rushed him.
Having secured top spot with a match to spare MacDonald opted to ring the changes and rest his incumbents for next week's quarter-final but the Blues always had confidence their young brigade would hold their own.
MacDonald can now sit back with a knowing smile. Not only has he banked the luxury of his frontline starters savouring a week off but exposing the future to such adversity, and seeing them emerge out the other side, will significantly boost their confidence, too.
Following a scrappy first half, the Waratahs changed gear and tactics in the second spell after finding no success with their lineout maul to give the ball some air. Two set piece strikes later and right wing Mark Nawaqanitawase had a double in six minutes to blow the game open.
Just when it seemed the Waratahs would kick clear, the Blues found a way to reel them in.
The result, for the Blues at least, has no bearing on next week's home quarter-final. Darren Coleman's Waratahs will now be forced to travel to Hamilton for their quarter-final.
The Blues attack was largely disjointed for the first half – hardly a surprise given the vast number of unfamiliar combinations thrown together.
Corey Evans offered a strong midfield presence but 20-year-old rookie first five-eighth Jock McKenzie endured a shaky outing as he lost the ball in contact, missed his first penalty attempt and was turned over with one carry.
With ball in hand direction was lacking as the Blues made several uncharacteristic errors. Sullivan, who moved into first-five for the final 25 minutes, hit three kicks, including one restart, out on the full, but he came good when it mattered most.
The Blues weren't helped by losing 20-year-old loose forward prospect Anton Segner to what appeared to be a serious ankle injury in the 12th minute, which injected Akira Ioane off the bench.
For the vast majority of the first half, the Waratahs set up camp inside the Blues half. The locals coaxed two yellow cards from the Blues – both in the loose forwards.
First Adrian Choat was caught in an unfortunate position with Waratahs halfback Jake Gordon falling into his attempted tackle and being caught high. Ioane then copped the second yellow a minute later for repeat team infringing as the Blues buckled, but refused to break, under relentless goal-line pressure.
Defensively, the Blues were superb. Through desperate scrambling efforts, committed, organised maul defence and multiple huge scrum shunts, where loosehead prop Jordan Lay led the charge with six men against eight, the Blues consistently repelled the Waratahs.
While their lineout disintegrated, the Blues scrum proved a weapon to earn two further penalties that allowed them to emerge 3-0 at the break, despite being reduced to 13 men and forced to live off 33 per cent territory.
That McKenzie's second penalty attempt broke the deadlock for the first points in the 37th minute speaks to the scarce attacking highlights.
As fatigue set in and both teams embraced more willingness to use the ball the game opened up.
The Blues again savoured impact from their bench, with Suafoa and Karl Tu'inukuafe adding punch that helped maintain their unbeaten surge.
With home advantage and momentum firmly in their favour, the Blues remain the team to beat.
Blues 20 (Cameron Suafoa, Luke Romano tries; Jock McKenzie pen, Zarn Sullivan 2 cons, drop goal)
Waratahs 17 (Mark Nawaqanitawase 2 tries; Tane Edmed 2 cons, pen)