Serena Williams kept alive her hopes of a record-equalling 24th Grand Slam singles title

Serena Williams kept alive her hopes of a record-equalling 24th Grand Slam singles title with a 4-6 6-3 6-2 win over Tsvetana Pironkova in the US Open quarter-finals.

The American six-time champion, 38, struggled early on with the variety of shots from the unranked player who was in her first tournament in three years.

The Bulgarian, 32, broke in the fifth game en route to taking the first set.

Pironkova tired as Williams took the second and broke twice in the third.

The veteran will now play former world number one Victoria Azarenka or Belgian 16th seed Elise Mertens.