Jorge Lorenzo has taken his fourth pole position of the 2009 MotoGP season during qualifying for the US Grand Prix at Laguna Seca, but finished the session in the back of an ambulance after a huge highside - a fate also shared by fellow title contender Casey Stoner.

Lorenzo's accident, which left the Fiat Yamaha star with what looks like right knee damage, was the Fiat Yamaha star's second heavy fall of the day, having previously lost the front of his factory M1 through the penultimate corner with 22 minutes to go.

Lorenzo's second accident took place at the same fast right-hander with just three minutes remaining, as he returned to the track to protect his pole position. This time the 22-year-old was launched high into the air after his rear wheel lost traction, then landed heavily on his right shoulder before tumbling through the gravel.

The #99 tried to stand up but couldn't put any weight on his injured leg and an ambulance was called. Later pictures showed a composed but clearly worried Lorenzo gesturing at his leg to Dr Costa of the Clinica Mobile and additional shoulder damage is a real possibility. Lorenzo crashed out of last year's US GP on the very first lap, injuring his ankle.

No sooner had Lorenzo's accident occurred than fellow title contender Casey Stoner, who had briefly taken pole from Lorenzo after his first fall, suffered an almost identical accident at the Turn Three right hander.

Stoner, already battling an undiagnosed energy-sapping illness, also hit the asphalt hard following a huge highside and had to be removed from the track on a stretcher. Fortunately he was later declared 'OK' and walked to the medical centre.

With his nearest championship rivals on the sidelines, world championship leader Valentino Rossi snatched second place - with a time 0.167sec behind Lorenzo - on his very last lap. Rossi, winner of the last two events, will start round eight five points in front of Lorenzo and nine ahead of Stoner.

Honda riders Dani Pedrosa, Andrea Dovizioso and Toni Elias have disputed fourth, fifth and sixth in both practice sessions, and that pattern continued in qualifying with Pedrosa's Repsol machine 0.435sec from Lorenzo and just 0.022sec in front of team-mate Dovizioso. Elias put his Gresini-run factory bike just 0.011sec behind Dovizioso for an all-RCV second row.

The leading American on Independence Day was Monster Yamaha Tech 3's Colin Edwards, but the 35-year-old looked mortified with his seventh position, 0.8sec from pole, at the end of the session.