Jorge Lorenzo's first non-finish since Australia 2009 cost him the MotoGP World Championship lead at Silverstone on Sunday.
The reigning world champion had taken the 2011 points lead with victory at round two in Jerez, when Stoner was brought down by Valentino Rossi.
But Stoner's speed was proving hard to contain and he had closed to within seven-points of Lorenzo heading into round six Silverstone, where Stoner took the lead on lap 2 of the soaking 20-lap race.
Determined to try and prevent the Honda rider winning his fourth race of the year, Lorenzo needed to overtake Stoner's team-mate Andrea Dovizioso as soon as possible.
Unfortunately for Lorenzo, his urgency resulted in a highside through the fast first turn, on lap 9 (pictured).
"I feel disappointed because the crash was my own mistake. It's a shame for the team because they did a very good job all weekend and also my Fan Club who come here to support me," said Lorenzo.
"I was riding with confidence, but I had to wait my moment to overtake Andrea. I think I could have fought for the victory with Casey. I wasn't worried that Simoncelli was catching me; I was worried because Casey was going if I didn't overtake Andrea... then I crashed!"
Having dropped 18 points from Stoner, Lorenzo believes he will now need to change tactics and go all-out for victory.
"Before Casey was chasing me, like a greyhound with a hare but now the situation has reversed. Now we have to go for the victory in Assen!" he declared.
Lorenzo's exit - shortly followed by that of Simoncelli - helped satellite Yamaha rider Colin Edwards claim a shock podium finish, just one week after breaking his collarbone.
"I want to say congratulations to Colin; it has been a good weekend for him. He deserves it after last week," said Lorenzo.
Lorenzo's team-mate Ben Spies also crashed out of the race.