Neptune Collonges became the first grey winner of the John Smith's Grand National since 1961 and added the only major prize missing from trainer Paul Nicholls' trophy collection in an excruciatingly tight finish at Aintree before being instantly retired.

But the thrilling finale was overshadowed by the fatal injuries suffered by the Jonjo O'Neill-trained Gold Cup winner Synchronised and According To Pete.

Synchronised was the focus of pre-race drama when he galloped off after jinking and dumping champion jockey Tony McCoy on the turf on the way to the start. He then fell on the first circuit of the four-and-a half-mile contest and had to be put down after suffering a broken hind leg.

At the finish, however, neither O'Neill, also the trainer of runner-up Sunnyhillboy, nor Nicholls, was sure of the result, the two horses having flashed past the post together before a margin of a nose was announced in favour of the 11-year-old 33-1 chance.

Neptune Collonges and Daryl Jacob had greater momentum than Richie McLernon and Sunnyhillboy (16-1), hauling himself over the line just in front to secure Nicholls yet another trainers' championship by a wafer-thin margin and help owner John Hales ease the pain of his most wretched Liverpool memory.

Hales, a key figure in the toy-making business, witnessed the death of his greatest horse and another grey, One Man, at this meeting in 1998.

He quickly announced the retirement of Neptune Collonges, who formed the admittedly lower-profile final member of Nicholls' outstanding chasing trinity, finishing third behind Denman and Kauto Star in the Gold Cup four years ago, as well as taking three Irish Grade Ones.

Jacob dedicated the win, the first by a grey since Nicolaus Silver 51 years ago, to his late best friend Kieran Kelly, a highly accomplished jockey himself. He said: "Kieran looked after me when I worked for Dessie Hughes and virtually kicked me out of the house to go and ride in England, so without him I wouldn't be here.

"It is the same with Robert and Sally Alner – I'm just happy to repay them for what they did.Nipper [Neptune Collonges] was going as fast at the start as he was at the end – he knew what pace he was going and I just trusted him on it. I don't think he missed a beat the whole way round."

Irish challenger Seabass, the 8-1 joint-favourite, had given Katie Walsh every possible chance of becoming a first female National winner until the final fence, but it was down to two serious contenders on the unforgiving run-in. Walsh, however, remains convinced that a female jockey will one day ride a National winner.

She said: "I had an unbelievable spin. It was a fantastic experience. It was great to get round. I can't believe it's all over and I can't wait to do it again. I was delighted to be placed."

Nicholls had saddled 52 previous runners, getting closest with runner-up Royal Auclair in 2005. He said: "I kept saying to my wife Georgie that [Neptune Collonges] was probably the best horse we've run in the race – if it wasn't for Kauto and Denman he would have won a Gold Cup.

"He's been placed in Gold Cups, he's won Grade Ones, he stays and he's genuine. Gold Cup form counts for an awful lot and Daryl went the brave man's route and little shortcuts make all the difference."

Nicholls went on: "It's obviously a great race to win, but we've not had the best of luck in it.

"We've won a first Champion Hurdle this year and I had given up on the championship after the day Nicky Henderson has had today, so it's a surprise. I'm not going to win it next year so we need to regroup.

"This was going to be his last race and he'll be retired now. He can go out in a field over the summer with Denman and Kauto Star and have a wonderful home for life. Good old Neptune."

Henderson had the solace of a superb four-timer at Aintree as his near 155-1 quartet of Simonsig, Sprinter Sacre, Oscar Whisky, all ridden by Barry Geraghty, and Lifestyle, with David Bass aboard, brought the stable about £200,000. However, it paled in comparison to the £547,000 earned by team Nicholls in the big race of the day.

Oscar Whisky (9-4) was the star of the Henderson show, repeating his victory in last year's John Smith's Aintree Hurdle.

He proved once again that the two-and-a-half miles around Aintree is his optimum, fighting off a sustained challenge by a neck from Thousand Stars, just as he did 12 months ago.

The champion hurdler Rock On Ruby was forced to make his own running due to the lack of a natural front-runner, and was still in front jumping the second-last but faded into third.