PARIS: Top seed Novak Djokovic passed his first real test at this year’s French Open with flying colours as he battled past Russia’s Karen Khachanov 6-4 6-3 6-3 on Monday to reach the quarter-finals for the 14th time. The 33-year-old claimed a fourth successive straight-sets victory in his latest quest for a second French Open title, but it was nowhere near as straightforward as the score suggests. Djokovic faced stiff resistance before taking the first set and had an anxious moment when his attempted return off one Khachanov serve ricocheted off his frame and struck a line judge in the head, reviving memories of his U.S. Open debacle. Khachanov saved four set points at 2-5 in the second set before Djokovic moved two sets clear. Djokovic appeared to be in cruise control when he led 2-0 in the third but Khachanov took the next three games and had two break points for a 4-2 lead. The Serb held, though, and regained control to ease into his 47th Grand Slam quarter-final where he will face either German qualifier Daniel Altmaier or 17th seed Pablo Carreno Busta, the man Djokovic was facing in the U.S. Open fourth round when he was defaulted for hitting a line judge with a ball.