Serena Williams hails Bethanie Mattek-Sands spirit following US Open scare

Serena Williams has paid tribute to Bethanie Mattek-Sands after surviving a big scare to beat her fellow American and reach the US Open fourth round this morning.

Williams, 33, was just two games away from seeing her hopes of a calendar Grand Slam go up in smoke, with the duo level at 5-5 in the second set after Mattek-Sands - ranked 101 in the world - won the opener 6-3.

The world number one ultimately levelled with a 7-5 win, before winning the decider 6-0 as the 30-year-old - who underwent a second hip surgery last year - failed to eliminate the defending champion.

"She's a great player," Williams told ESPN afterwards.

"She's fought through so many difficult injuries. I admire her for all that she's been through. She's always so positive. It was a really good match for her today as well."

The defending champion will take on Madison Keys in the fourth round.