Round four of the 2015 FIA World Endurance Championship, the Six Hours of Nürburgring, got underway on Sunday on the Grand Prix circuit at the German track. Here's what happened during the opening three hours of racing.

First Hour

The start didn't see big changes in the lead of each class. Neel Jani was leading in the No. 18 Porsche Team car with all other LMP1 cars remaining in their qualifying position, apart from the No. 13 Rebellion Racing car that had pitted from the formation laps and couldn't start the race.

Nick Tandy was leading LMP2 in the No. 47 KCMG Oreca-Nissan and Gianmaria Bruni was at the front of the GTE-Pro class in the No. 51 AF Corse Ferrari. The only change in class lead at the start was in GTE-Am where No. 77 Dempsey - Proton Racing Porsche, driven by Patrick Long took the class lead after starting third on the grid.

After only nine laps, the GTE-Pro class-leading No. 51 AF Corse Ferrari stopped on track, causing the first full-course yellow of the race. James Calado in the No. 71 sister car inherited the class lead. The Ferrari's lead was short-lived, though, as it pitted during the full-course yellow period and Michael Christensen in the No. 91 Porsche Team Manthey car took the GTE-Pro lead.

During the first stops after 40 minutes of racing, the second-placed No. 17 Porsche had its nose changed, allowing the fourth-placed No. 7 Audi Sport Team Joest car that pitted simultaneously get past. The No. 8 Audi that had been between those two pitted a few laps later but joined the track behind them, continuing in fourth place after the cars ahead pitted. In LMP2, the No. 47 KCMG car continued in the lead after the opening round of stops.

Second Hour

At around an hour into the race, the remaining No. 12 Rebellion Racing car stopped and had to retire from the race. About 10 minutes later, the No. 17 Porsche overtook the No. 7 Audi to give Porsche again a 1-2 lead.

Meanwhile, the GT cars had made their first pit stops. The No. 91 Porsche continued in GTE-Pro lead whereas the No. 88 Abu Dhabi-Proton Racing Porsche had taken the GTE-Am lead.

The No. 18 Porsche was leading by about half a minute after one and a half hours of racing before it was issued a five second stop-and-go penalty for excessive fuel consumption. After serving the penalty, driver Marc Lieb exited the pits right ahead Mark Webber of the second-placed No. 17 sister car, though lost the lead when battling against Webber in the first corners of the lap. Lieb continued pushing Webber for the following two laps before Webber pitted from the lead.

The No. 18 Porsche came to its second scheduled stop seven laps later. With the fresh tires, Brendon Hartley's pace in the No. 17 Porsche had been good enough to comfortably get past the pitted No. 18 that joined the track on second place. By this point of the race, the Toyota Racing cars were so far off the lead that the Porsches and Audis ahead were able to pit without falling behind the Toyotas.

Meanwhile in LMP2, the No. 26 G-Drive Racing Ligier-Nissan had passed the earlier class leader No. 26 KCMG car during the second pit stops.

Third Hour

The No. 91 Porsche continued in the GTE-Pro lead by almost half a minute to the No. 71 AF Corse Ferrari. It was able to use a full-course yellow for its second pit stop, reducing the time loss.

After two hours and 15 minutes, the No. 18 Porsche was issued another penalty for excessive fuel consumption, this time a 30-second stop-and-go. The penalty dropped it to fourth place, behind the Audis. The issue with a faulty sensor stayed and soonafter that it was penalized yet again, that time for 60 seconds.

In the closing 10 minutes of third hour, the third full-course caution came out as Pierre Kaffer in the Team Bykolles LMP1 entry lost his rear wing, leaving debris on the track. Additionally, contact between the Abu Dhabi - Proton Porsche and the No. 71 Ferrari just after the yellow had come out left the Ferrari a bit damaged.

The Six Hours of Nürburgring continues until 7:00 pm local (1:00 pm ET). Follow @VAVELSportsCar on Twitter for live tweeting during the remaining half of this German round of the 2015 championship.

Kalle Tyynelä is a writer for the VAVEL USA Racing section. Follow him on Twitter at @FINdyCar.