Dennis' performance was good enough to make him the overall leader. 

Jan Barta (NetApp-Endura) posted an early standard with a 38:30, but with Martin already on the course, the Czech did not expect to be in the lead long. And so he was not. The German was 0:32 faster than Barta at the first checkpoint en route to the lead, and ultimately, the victory.

Other riders who posted excellent times were already on the course as well. Jonathan Castroviejo (Movistar) finished fourth at 1:08, and Robert Kwiatkowski, Martin's teammate, took fifth at 1:13. The Pole's performance put him in third place on GC.  

Who did not ride well was as important as who did. Joaquim Rodriguez (Katusha) is no rider against the clock, but no one expected him to lose nearly four minutes to Martin. The Spaniard is no longer in the GC picture.

Surprisingly, neither is Alberto Contador (Saxo Bank-Tinkoff). The former Tour de France winner was 1:09 behind Martin at the first checkpoint, and he continued to hemorrhage time, ultimately losing 3:38 to the world time trial champion. The Spaniard said that he was suffering from allergies, but before the race began rumors abounded that Contador was struggling to find his form. Today's performance did not give the lie to the rumors.

Alejandro Valverde (Movistar) is not a great time trialist, but he did not expect to lose three and a half minutes to Martin. His GC hopes have dimmed as well.

David Veilleux (Europcar) rode hard but could not ride well enough to keep the yellow jersey. The Canadian finished 76th and fell to seventh on GC.

Sky put four riders in the top ten: Froome (third at 0:52), Edvald Boasson Hagen (sixth at 1:19), Richie Porte (seventh at 1:20), and Geraint Thomas (10th at 1:42). The team's performance revealed its strength as the race enters the mountains where it will be decided.

Martin's ride revealed excellent form during the run-up to the Tour de France, which begins in three weeks. "I was really looking forward to today," he said. "It was the first long time trial after Volta ao Algarve. It was a really nice form test for the Tour. In the past days, I had some stomach problems due to a virus. The biggest problem I had was two days ago, and yesterday I was already feeling better, not 100 percent, but when I woke up this morning I was pretty OK, feeling optimistic and feeling confident. So, I'm not 100 percent recovered, but almost. I'm happy with the stage win."

In the overall, Dennis leads Froome by 0:05 and Kwiatkowski by 0:26. Stage 5 could change the standings. The 139-km ride from Gresy-sur-Aix to Valmorel will feature a Category 3 ascent and two Category 4s, as well as an hors categorie climb to the finish. Who will win? Will the standings change? Check in at www.roadcycling.com and find out!