The celebrations for Mascot's first career win have been short lived at Randwick thanks to Blake Shinn lodging a successful protest.

Shinn argued Koby Jennings on Mascot caused interference near the 150m mark of Monday's Summer Hospitality Plate (1400m) with Snitzel Day crossing the line a short half head behind.

Racing NSW stewards agreed and promoted the Chris Waller-trained colt to his maiden win while Mascot was relegated to second.

Stella Victoria was a neck back in third.

Tye Angland, who rode the Waller-trained Balearic, also protested unsuccessfully against the initial winner, saying he was impeded by Snitzel Day after that horse came into contact with Mascot.

Shinn said Mascot shifted out to take Snitzel Day off his line, requiring him to rebalance.

"If it didn't happen it's pretty clear he would have won the race," Shinn said.

Mascot's co-trainer Michael Hawkes acknowledged Mascot had shifted out, but said the incident was inconsequential.

"I believe every horse has had their chance to run him down. It's a 400-metre straight. Yes we have marginally shifted, but he was there to be beaten," he said.

Deputy chief steward Philip Dingwall disagreed, telling Shinn in the stewards' view Snitzel Day would have won had he not been impeded.

"Taking into account the manner of which your mount finished off the race strongly, your objection can be upheld," he said.

The reversal gave Waller and Shinn a double after Savacool claimed the Happy New Year Handicap (1800m).