Williams fights off Halep to reach U.S. Open semi-finals

Open on Wednesday but still could not stop the world number one from advancing to the semi-finals of the year's final grand slam.

The scrappy fifth seeded Romanian managed to take the first break points from Williams during the Flushing Meadows fortnight and the only set surrendered by the top seed but at the end of the day the result was the same, the 34-year-old American walking off court with a 6-2 4-6 6-3 win.

What had appeared to be a straight sets stroll into the last four for Williams turned into a tense battle when Halep dug in during a wildly entertaining second set that saw the Romanian fend off all 12 break points she faced.

But Williams, playing in her 46th grand slam quarter-final, would not be shaken and took the only break to go up 3-1 in the decider and then serve out for the win.

Williams will now face 10th seeded Czech Karolina Pliskova, a 6-2 6-2 winner over Croatian teenager Ana Konjuh, for a place in Saturday's final.