Racing:Tony McCoy's new association with Denman came to a premature end as the pair parted company at the third-last fence in the Aon Chase at Newbury.
After putting in a practically perfect round to five out under his intended Cheltenham Gold Cup rider McCoy, Denman clattered the fourth-last and was lucky not to unship the champion jockey.
However, he met the next fence all wrong again and McCoy could not hold on this time and tumbled out of the plate. That allowed stablemate Tricky Trickster to just edge out Niche Market in a thrilling finish.
Denman had been prominent throughout and looked to have built up a good rapport with his new partner as the 2008 Gold Cup hero put in a few of his trademark spectacular leaps.
The pair pulled clear turning into the straight but Niche Market was trying his best and making up a little ground coming down to the fourth-last.
Denman hit that one hard and as McCoy tried to regain his momentum, the third-last just seemed to come too quickly and the 10-year-old barely picked up at all, giving the 14-times champion no chance of keeping the partnership intact.
Stablemate Tricky Trickster found a second wind for Ruby Walsh and flew up the straight to peg back Niche Market.
The latter did his best but had no reply with Tricky Trickster prevailing by a short head at odds of 8-1.
Bookmaker reaction was swift, with Victor Chandler cutting Tricky Trickster to 12-1 favourite for the Grand National. Niche Market is 14s from 20s for Aintree.
The same firm cut Kauto Star to 4-5 from 5-4 for the Gold Cup, while pushing out Denman to 3-1 from 2-1. Tricky Trickster is 25s from 50s.
Nicholls reported Denman to be none the worse for his spill straight after the race.
"It's a job to see (what happened) from here," he said. "The main thing is that he's 100 per cent okay. He's not in distress and there's not a mark on him.
"He just made a mistake and then another - but we'll get him back, we've been there before."
Walsh admitted Denman's departure had caught him unawares. "I'm a bit shocked really," he said. "I didn't think AP (McCoy) looked overly happy with him throughout.
"My fellow has beaten the Irish National winner in Niche Market and I loved the way he jumped.
"He jumped super and really stuck his head down when I asked him to."
Nicholls added of the winner: "It's amazing how he got knocked at Fontwell on his return over hurdles but I told everyone he'd come on for the run.
"Once Denman had gone he stayed on and picked up. His next run will be the Gold Cup."