Sydney apprentice Deanne Panya's hard work has been the catalyst for her biggest career win on Testashadow in the $1 million Magic Millions Cup (1400m).

Panya gave the Gary Portelli-trained Testashadow ($31) the run of the race before hitting the lead in the straight and then holding on in a thrilling four-way finish.

A nose separated Testashadow from second placed Perfect Dare ($61) with a further nose to Snippets Land ($8) in third and another nose to Off the Rails ($31) in fourth place.

Panya, 22, who is in a close tussle with James Innes and Andrew Adkins in the Sydney's apprentice's premiership, rides a lot of work for Warwick Farm trainer Portelli who is a loyal supporter.

"Deanne rides this horse very well and they have combined for a couple of wins. I had no hesitation in putting her on for this race," Portelli said.

"She responded with a perfect ride. To be honest I would have been happy with second, third or fourth but I am a lot happier now."

Testashadow was second in the 2015 Magic Millions Guineas to Deiheros and has now won $1.18 million.

Portelli said Testashadow carried the colours of a cervical cancer charity as one of the owners was battling the disease.

Panya and her twin sister Beany were born in Sydney to Laotian parents who had never seen a racehorse but both girls became jockeys.

"We got a good position early on and from there he travelled beautifully in the run," Panya said.

"I was always stalking the leaders and when the gap opened he tried hard all the way at to the line."

Jim Byrne, who rode Perfect Dare, said the gelding's run was a marked improvement on his previous effort.

Brad Rawiller, who rode last year's winner Lucky Hussler who finished seventh, said his mount lost his momentum on the home turn and with 61kg it ruined his chances.