Serena Williams of the U.S.A. shakes hands with Victoria Azarenka of Belarus after winning their match at the Wimbledon Tennis Championships in London, July 7, 2015. [Photo/Agencies]

LONDON - The heavy hitting shook the ground and the volume would have raised the Centre Court roof, had it been closed, as Serena Williams and Victoria Azarenka traded blows like a couple of prizefighters at Wimbledon on Tuesday.

A women's tournament that has seen title contenders fall feebly on the All England Club lawns, finally witnessed two grand slam champions going toe-to-toe in a thunderous encounter befitting the final, rather than the second Tuesday.

Williams eventually won 3-6 6-2 6-3 with her best tennis at this year's tournament so far to stay in line for a sixth Wimbledon title which would also complete the self-styled "Serena Slam", that is holding all four majors concurrently.

"I feel really vulnerable. I feel really vulnerable in a third set," Williams, who looked anything but, told reporters. "At that point I kind of relax and whatever happens, happens."