This noble sport can often be distilled to a matter of weights and measures.

On Saturday Charlie Appleby runs Old Persian in the William Hill St Leger at Doncaster and once again he will meet one of Aidan O’Brien’s stars.

Last month Old Persian beat Kew Gardens by one and three-quarter lengths, in the Great Voltigeur Stakes at York, but Kew Gardens will be 2lbs better off at the weights for the St Leger.

There was plenty of interest when Appleby became a trainer for Godolphin in 2013. He was taking over from Mahmood al Zarooni, who was banned for doping offences, and some may have been surprised when he was chosen.

However, Sheikh Mohammed, the driving force behind Godolphin, knew Appleby well from his 15 years at the yard as travelling head lad, stable head lad and assistant trainer. The sheikh took a punt on Appleby but it paid off when Masar won the Derby, a first in the peacock-blue silks.

“The Derby is the ultimate goal,” Appleby said. “And with Masar being a home-bred and with His Highness Sheikh Mohammed and the royal family being there it was a very special day that will live with me forever.”

Those special days are what Godolphin was conceived for and next up is the St Leger which has been the long-term target for Old Persian, who has been something of a slow-burner. He was never going to be ready for the Derby and got caught out in the tactical battle of the Irish Derby but Appleby is happy with his progress since.

“He’s a typical Dubawi, just progressing with age. We put a line through the Irish Derby because the race just didn’t work out as we’d planned in that we thought they’d go a decent gallop and it didn’t materialise that way. We just found ourselves in the wrong position.”

Old Persian was in the right position at York, with Kew Gardens in third, and leaving a rather subtle conundrum for the form experts and punters. Will the 2lb weight concession that Kew Gardens had to make that day be enough to erode the margin of that defeat or has Old Persian more to give?

The theory will be put to the test in that brutal chome straight at Doncaster.

“Kew Gardens is favourite and he is the Group One winner,” Appleby said. “And the racereaders may say that he was doing his best work at the end. But the one thing about Old Persian, he wasn’t for stopping – he had every opportunity. We had Cross Counter [the runner-up] in there as well and James [Doyle, the jockey who rode Old Persian] said that when Cross Counter came to him, there was no way he was going to get past. He just found again and James knew in the last 50 yards he had Cross Counter covered. And he takes all the experience into a race like the Leger that you need.”

Appleby still has both Loxley and Brundtland in the St Leger and, while they may lack experience, neither looks short on potential with Brundtland appearing a possible for next year’s Gold Cup at Royal Ascot.

That could also be a race for Cross Counter who, as a gelding, is ineligible for the St Leger, but will contest the Melbourne Cup in Australia in November.

If the weight of expectation bears down on Appleby’s shoulders he does not show it, which is probably the measure of the man.