By Steve Keating

NEW YORK (Reuters) - World number one Novak Djokovic scrapped his way into the U.S. Open final for a seventh time on Friday with a confounding 6-3 6-2 3-6 6-2 win over enigmatic Frenchman Gael Monfils.

Often viewed as more showman than competitor, the 10th-seeded Monfils tested the patience of both Djokovic and the fans with a display of tennis that swung wildly from dynamic to indifferent.

With Monfils showing little interest and even less effort in dropping the opening two sets on a hot and muggy day, the unhappy Arthur Ashe Stadium fans voiced their displeasure as they showered the Frenchman with jeers and boos.

But when trailing 2-0 and a break down, the player who reached the semi-finals without dropping a set suddenly appeared as Monfils battled back to take the third set.

Djokovic will take on either Swiss third seed Stan Wawrinka or sixth-seeded Japanese Kei Nishikori in Sunday's final in his bid to become the first back-to-back winner at Flushing Meadows since Roger Federer won four straight from 2004.

(Editing by Mark Lamport-Stokes)