Halfway to Heaven was the less fancies of O'Brien's two runners
Irish trainer Aidan O'Brien claimed his 21st Group One win of the season as 8-1 shot Halfway to Heaven won the Sun Chariot Stakes at Newmarket.
The Irish 1,000 Guineas winner, ridden by stable number two Seamus Heffernan, shocked hot favourite Darjina.
Meanwhile, the 25-1 chance Tazeez landed the Cambridgeshire Handicap to seal an 884-1 double for John Gosden.
Earlier, Yeats was beaten at the Arc meeting while 2005 Cheltenham Gold Cup winner Kicking King fell in Ireland.
French filly Darjina, second in all five of her previous races this season, was the bridesmaid again in the Sun Chariot Stakes.
Trainer Alain de Royer-Dupre, who runs the well-fancied Zarkava in the Prix de l'Arc de Triomphe at Longchamp on Sunday, was looking for a winning start to his Arc weekend.
But just as in the Arc, the French trainer faced a challenge at Newmarket from his Irish counterpart O'Brien, who saddled both Listen and Halfway to Heaven.
And O'Brien secured further Group One glory as he chases a world record 26 wins at the highest level in one season.
At Longchamp, he ran Yeats in the Prix du Cadran on day one of the Arc meeting.
But the triple Ascot Gold Cup winner, who was odds-on to give O'Brien a Group One win in France, could only finish fifth behind 16-1 shot Bannaby.
There was a surprise in the Cambridgeshire Handicap at Newmarket as Tazeez completed a memorable day for trainer Gosden, who earlier won the Tattersalls Timeform Million with Donativum (33-1).
Ridden by Richard Hills, after original pilot Martin Dwyer switched mounts, the gelding hung on to beat 66-1 outsider Nanton.
Favourite Swop appeared to come with a winning run but had to settle for third, while Little White Lie was fourth.
In Ireland, Kicking King fell on his seasonal debut as Knight Legend won the Gowran Park Champion Chase.
Kicking King, a dual King George VI Chase winner, came back from a career-threatening injury last season, but has mainly disappointed trainer Tom Taaffe since his return.
Totesport.com Cambridgeshire, Newmarket 1m 1f
1 Tazeez (R Hills) J Gosden 25-1
2 Nanton (R Hughes) 66-1
3 Swop (R Hughes) 7-1
4 Little White Lie (MJ Kinane) 25-1
28 ran. Dist: 1, 1¼
Kingdom of Britain Sun Chariot Stakes, Newmarket 1m
1 Halfway To Heaven (JA Heffernan) AP O'Brien 8-1)
2 Darjina (R Hughes) 11-10 fav)
3 Visit (A Munro) 20-1
10 ran. Dist: ½, 1.
Prix du Cadran, Longchamp 2m 4f
1 Bannaby (C Soumillon) M Delcher Sanchez 16-1
2 Incanto Dream (Y Lerner) 18-1
3 Orion Star (J Victoire) 40-1