Kizlyar (25/1) led home a one-two for Joseph O’Brien in the Ascot Stakes following a sustained battle with stablemate Defiantly over the final two furlongs.

Having saddled the second, third and fourth in the staying contest 12 months ago, O’Brien fielded a seven-strong team, with one of the biggest-priced runners in his squad coming out on top.

Kizlyar led narrowly a furlong out and kept finding to give his rider Joey Sheridan a first Royal Ascot success. Defiantly (25/1) went down by a head, with Tim Toe (8/1) third for last year’s winning trainer Henry de Bromhead. Barnso (40/1) fared best of the British runners in fourth.

Joseph O’Brien said: “Kizlyar is off the back of a good win last time. We didn't get into the Fred Winter, unfortunately. This was obviously the next target for him, and I'm delighted to win such a good race with him.

"I am so delighted for Margaret and her family – they lost Dr Andrew Heffernan, Margaret's husband, a few months ago, and I feel like Kizlyar had a little extra push in the final 100 yards. It looked like Defiantly maybe had outbattled him at one stage, but he battled back hard in the final furlong.

"He might be one to go abroad with – we'll see what the handicapper does and go from there."

Margaret Heffernan, who set up the H O S Syndicate for her grandchildren, said: “Today is special because I lost my husband Andrew 12 weeks ago and this was his week. The idea of the syndicate with the grandchildren was really his; he believed in it and he believed in Joseph so much.

"We've had some great luck. I've been in horses all my life but never had the luck like we've had since the syndicate started, and it's fantastic for the grandchildren. He would be absolutely thrilled. We had two winners last year at Ascot, but this year is obviously very special and we have more grandchildren than ever.

"I said to Joseph, 'he would be so delighted for you as well' – he's been fantastic. It is an amazing syndicate. I have two groups of grandchildren, older and younger, and for the older ones especially it has been such a success. Some of them had never come racing before and it's brought us all together. They're at different stages of their lives, all parts of the world, and they're all here today."

Sheridan said: “I didn't know if I had won. My right arm got caught up with James Doyle on Defiantly, and I thought Defiantly had come back at me. But I knew this lad would stick his head out, so when I got my right arm back out of a tangle with Jame, I just put it down. In fairness to him, he was so genuine – when I asked him to put his neck down for me at the line, he did.

"It just means everything – my first win at Royal Ascot. I only started riding for Joseph O'Brien last year and it's what kept me in Ireland really. I can't thank him enough for what he's given me. Dylan Browne McMonagle was out for the first two months of the season and Joseph fired everything at me, so to pay him back with a Royal Ascot winner is brilliant."