Leading Light won the Gold Cup in a thrilling finish on Thursday, denying Queen Elizabeth II's horse Estimate a second consecutive victory in Royal Ascot's most prestigious race.

The four-year-old Leading Light, the 10-11 favorite, surged ahead in the final straight of the 2-1/2-mile event to beat Estimate (8-1) by a nose and give trainer Aiden O'Brien a record sixth Gold Cup win.

Outside shot Missunited (40-1) took third by half a length.

Missunited set the pace from the start. Estimate looked in contention for back-to-back victories on the home turn but was kept in by Leading Light. The filly had to go for a run up the inside, and the favorite prevailed.

"Ryan (Moore, on Estimate) was looking for a bit of room, but I was entitled to keep a straight line," said Leading Light jockey Joseph O'Brien, son of the trainer. "When you win, it is always a good ride. There's no such thing as a bad winning ride. Ryan gave me a bit of help by coming up my inside as he pushed me along a bit. This fellow is as tough as nails."

Aidan O'Brien celebrated his second win of the day after Joseph guided Bracelet to win the Ribblesdale Stakes.

"He's idle, but he was in a lovely position and settled well," O'Brien senior said of Leading Light. "He was very lazy when he got there. Joseph was trying to keep him with company."

Estimate won last year's race for the Queen to become the first reigning British monarch with a winning horse in Royal Ascot's biggest race. But her preparation for the defense of her title was hampered by a muscle problem, and Michael Stoute's mare made only her first start since October on Thursday.

"It was a great run, and I'm very proud of her," trainer Michael Stoute said. "It's been a great team effort back at home to get her back on the track after so long, but she's made it easy for us, as she's a very brave filly."