NEW YORK (Reuters) - Young Frenchman Lucas Pouille scored a stunning five-set upset over 14-time grand slam singles winner Rafael Nadal, winning a climactic tiebreaker 8-6 to reach the US Open quarter-finals on Sunday (Sept 4).

Displaying poise beyond his years, the 22-year-old Pouille took charge early and led two sets to one, then rebounded after sagging in the fourth set to win 6-1, 2-6, 6-4, 3-6, 7-6(6) in a four hour, seven minute struggle against the fourth seed.

Playing in his third consecutive five-set match, 24th seed Pouille, still looking for his first ATP Tour title, showed that his quarter-final advance earlier this season at Wimbledon was no fluke.

"I couldn't dream better than this," he said in an on-court interview after falling flat on his back in celebration when his forehand winner ended the marathon on his fourth match point.

Pouille will play 10th-seeded compatriot Gael Monfils in the last eight.

Monfils advanced with a 6-3, 6-2, 6-3 victory winner against unseeded Marcos Baghdatis of Cyprus, and has yet to lose a set in the tournament.