The pair were sublime across the the 161-lap journey, a tyre scare in the first half of the race, and a dicey moment battling the Triple Eight cars in the second, the only hints of trouble for the #25 WAU Holden.
In the end the car had unbeatable pace, Mostert able to hold off reigning Great Race winner Shane van Gisbergen in a straight fight across the last two stints.
Mostert is now a two-time Great Race winner, this latest triumph joining his remarkable 2014 crown.
For Holdsworth this is a maiden Bathurst 1000 victory, his fourth career race win and first win since 2014.
It’s Walkinshaw Andretti United’s eighth Bathurst 1000 win and first since Garth Tander and Nick Percat in 2011.
Holdsworth led into the second half of the race before pitting on Lap 92 to kick off his final stint of the race.
That left James Moffat leading Garth Tander, the pair running nose-to-tail until Lap 99 when Moffat pitted to hand over to Cam Waters.
Tander did likewise to give Shane van Gisbergen the #888 Holden a lap later as Holdsworth filtered back into the lead of the race.
Five laps later the safety car made its second appearance of the race for the most bizarre of reasons – an echidna on the circuit.
Holdsworth used that opportunity to pit and hand over to Mostert, who resumed behind van Gisbergen behind the safety car.
Jamie Whincup wound up third in the queue, which led to some fascinating formation flying from the Triple Eight cars a lap after the restart.
Mostert tried to round up van Gisbergen into Griffins, the Kiwi instead hanging Mostert wide so that Whincup could sneak through at the Cutting.
Anton De Pasquale followed Whincup through, while Brodie Kostecki pulled an incredible move inside Cam Waters on the way to the Metal Grate for fifth.
Mostert got back into third on Lap 112 by passing De Pasquale into Murray’s, right before the safety car was called again when Jayden Ojeda hit the wall.
That prompted a wave of stops, Whincup the big loser as he had to stack behind van Gisbergen.
Mostert, meanwhile, was the big winner as he short-filled to jump van Gisbergen.
The #25 was behind and out-of-sync David Reynolds for the restart but was able to quickly charge back into the lead.
On Lap 121 the safety car made its fourth appearance when Jake Kostecki hit the wall at the Elbow.
The race went green again on Lap 125, Mostert leading van Gisbergen and Brodie Kostecki in what had boiled down to a straight fight to the flag.
Mostert did his best to bolt in the laps that followed, lowering the fastest lap several times as he built a gap of 2.5s over van Gisbergen.
The gap was more like five seconds by the time Mostert came in for his final stop of the race on Lap 138.
Van Gisbergen followed suit a lap later, almost clouting the wall on the way into the lane. He re-joined behind Mostert, as Waters jumped Kostecki out of the lane.
On Lap 140 the safety car was called for a fifth time when De Pasquale rolled to a stop in the Cutting with a suspected driveline issue.
The race went green on Lap 142 but only briefly, Broc Feeney – who was running an impressive ninth – smacking the wall at Sulman Park.
That sparked safety car number six before the next restart on Lap 145.
Once again Mostert had the pace to gap van Gisbergen, who looked as if he was going to have to settle for second.
That was until the Kiwi’s right-front tyre delaminated seven laps from home, van Gisbergen sinking through the field as he limped back to the pits.
His slow run across the top led to a hairy moment for Kostecki, who tagged the wall at McPhillamy Park as he swept past van Gisbergen for third.
All of that was great news to Mostert, who was left nearly four seconds down the road from Waters as he cruised to victory.
Waters and James Moffat finished second despite a fuel consumption scare due to a faulty sensor in the final stint.
Kostecki and David Russell were third, as Whincup and Craig Lowndes grabbed fourth in what is Whincup’s final race as a full-time driver.
Bryce Fullwood and Warren Luff finished a fine fifth to cap off an incredible day for Walkinshaw Andretti United ahead of Nick Percat and Dale Wood.
James Courtney and Thomas Randle finished a remarkable seventh after a neat recovery from Randle being beach in the Hell Corner sand trap early in the race.
Todd Hazelwood/Dean Fiore, Tim Slade/Tim Blanchard and Will Davison/Alex Davison rounded out the Top 10.
Van Gisbergen and Tander were classified 18th.
Bathurst 1000 – Race results:
Race results to follow