The breakdown of Cylinder Beach has marred the win of Single Gaze in the Group Two PJ O'Shea Stakes (2200m) at Doomben.

Single Gaze won the O'Shea in emphatic fashion amid distressing scenes when Cylinder Beach suffered a fatal injury near the 200m.

Cylinder Beach was looming as a winning chance when he faltered and was quickly eased down by jockey Jim Byrne.

Trainer Desligh Forster sprinted to Cylinder Beach's side to attend to the gelding and was later inconsolable when she returned to the enclosure.

Stewards confirmed Cylinder Beach was euthanised after breaking down in the near fore fetlock.

Winning trainer Nick Olive admitted to experiencing mixed emotions after the O'Shea.

"You hate to see that sort of thing happen in a race and I feel very sorry for the connections and trainer of Cylinder Beach," Olive said.

"We've won a Group Two and I suppose we need to be positive about that."

Olive praised Single Gaze's consistency and will-to-win.

"For a country trainer to get a horse of this quality and to have this mare turn up every time is a pretty rare thing," he said.

"I don't think I'll get another one quite like her. We forget she ran third in the Magic Millions, raced in the Slipper as a two-year-old and now here she is winning Group Two weight-for-age races."

Olive said Single Gaze is likely to miss next Saturday's Brisbane Cup and be aimed instead at the spring carnival in Melbourne.

The Caulfield Cup is high on a list of races Olive will consider for Single Gaze who has battled injury to make it back to the races following a fall in last year's ATC Australian Oaks.

"She had deep-seated bruising which took a long to get over but it's good to see her back winning races again," he said.

Winning jockey Kathy O'Hara was confident Single Gaze would win when she was cruising outside the leader, Preferment, before hitting the lead on the home turn.

"I could see Hughie (Bowman) getting busy on Preferment down the side of the track and I knew I had a lapful of horse underneath me," O'Hara said.