Stratum Star has provided Craig Williams with his fifth Sir Rupert Clarke Stakes win, continuing a family affinity with the race for the high-profile jockey.

The Darren Weir-trained Stratum Star's victory by the barest margin over Disposition in a thrilling three-way finish to Saturday's Group One 1400m handicap at Caulfield added to an impressive record in the race for Williams over the past decade having first won the event in 2005 on Barely A Moment.

Williams' father Allan also won the race as a jockey in 1979 on Private Talk and again as a trainer in 1993 with Black Rouge.

Stratum Star had a wide barrier to overcome and Williams sent the horse forward to settle on speed before getting a trail behind Strawberry Boy and Rich Enuff.

Under The Louvre made his charge on the outside of Stratum Star in the straight and hit the front while Damien Oliver brought Disposition through close to the inside which set up a tight finish.

Stratum Star ($9) surged again after losing momentum and in a head-bobbing finish got home by a nose over Disposition ($4) with Under The Louvre ($5.50) a half head away.

Williams thought he had won but the judge took several minutes to declare a winner.

The talented Stratum Star gave Victoria's premier trainer Darren Weir back-to-back wins after Trust In A Gust scored in a photo finish a year ago.

"He was awesome today," Williams said of Stratum Star.

"Credit to Darren Weir and his management of this horse. This is the race they had picked out. They wanted to get a Group One for him and they've done it."

Weir said the race had been a long-range target with four-year-old Stratum Star.

"I thought he had had a good preparation going towards it and he got a terrific ride from Craig," Weir said.

"If we didn't get that sort of ride, he probably wouldn't have won the race.

"He loomed up last start to win (the Memsie Stakes) and just got a bit tired with 50 metres to go, so then we really targeted this race."

Stratum Star's head-bobbing win denied Disposition's jockey Damien Oliver his seventh victory in the event.

"He has run a good race, but unfortunately we just missed," Oliver said.