Serena Williams dug deep to keep alive her hopes of a calendar Grand Slam by surviving a major scare to beat Heather Watson and move into the last 16 of Wimbledon this afternoon.

Watson looked on course to record a significant upset by recovering from a set deficit to go within one game of beating the world number one.

However, the American, vying for a fourth successive Grand Slam, ultimately edged the victory 6-2 4-6 7-5 in an epic battle that lasted two hours and 17 minutes.

As the last Briton standing in the ladies' singles, Watson was the crowd favourite on Centre Court, but the fervent support did little to unnerve the 20-time Grand Slam champion.

There looked to be a gulf in class between the duo in a fast and furious opening set that saw Watson struggle with the power of her American counterpart.

Williams inflicted one break of serve in the fourth game to move 3-1 up, and another in the eighth to seal a first-set lead in comfortable fashion.

However, Watson pulled out a break of her own in the fifth game of the second set to move 3-2 up - a gesture that only served to rile Williams, who broke straight back.

With Williams 4-3 ahead, it seemed that she was heading toward victory, but Watson dug deep to hold her serve and then break once more en route to a 5-4 lead, before serving out the set.

Two further breaks of serve in the first three games of the deciding set saw Watson move 3-0 ahead and halfway toward the biggest victory of her career.

Nevertheless, Williams, who had a 23-game Grand Slam winning streak to protect, with her last major defeat coming at Wimbledon last summer, broke back in a gruelling fourth game that spanned almost 15 minutes, before holding serve to move 3-2 behind.

Another break helped her level up the set, before both held their respective serves to leave the pair with four games apiece heading into what promised to be a thrilling finale.

Watson brought the thousands of fans inside Centre Court to their feet by breaking the Williams service once more to move within one game of victory, but it proved a false dawn as the American won the next two to snatch a hard-fought win.

Williams will meet sister Venus in the fourth round, after the five-time champion beat Aleksandra Krunic earlier today.