Novak Djokovic's serene progress through the French Open continued as he reached the quarter-finals with a straight sets win over Jan-Lennard Struff. The World No.1 is still yet to drop a set as he bids to win a second Roland Garros title, and recorded a 6-3, 6-2, 6-2 victory over the German. The first set was the tightest of the three, with Struff going toe-to-toe with Djokovic until the sole break in the penultimate game. That sparked a run in which Djokovic won seven straight games, helping him to claim the second set 6-2. In the final set, the Serb again ran into a hefty lead as he coasted through to the last eight. "Obviously these kind of conditions favour my game against his," he told Eurosport. "It's very heavy, very muddy, it slows down. His big weapon is his serve and I managed to get a lot of serves back. It's completely different playing him in these conditions to when it's 35 degrees and sunny. Rain like this is characteristic for Paris at this time of year."