Serena Williams came through a titanic three-set tussle with Alison Riske to take another step towards an eighth Wimbledon title.

A hard-fought 6-4 4-6 6-3 victory in the all-American showdown on Centre Court ensured the 37-year-old reached her 12th semi-final in 19 appearances at the Championships.

For Riske there was no reward despite five breaks of serve – converting every single break point she created – against the 23-time grand-slam winner.

Riske, unseeded and ranked 55 in the world, had knocked out top ranked Ashleigh Barty 24 hours earlier, and she pushed Williams all the way.

Riske made a brisk start, securing the first break of serve for 2-1 despite Williams crashing down three aces.

Three games later Williams forced three break points, yet squandered the second by not challenging when her ball was called long but was, in fact, well in.

Instead she converted at the fourth attempt to level the match, before the pair exchanged further breaks. Neither player was serving badly, but both were returning superbly.

Williams stepped on the gas by holding to love and, in the crucial 10th game two Riske errors gave her two set points.

The underdog saved the first but then opted to swing at a high ball which looked likely to land out, and succeeded only in planting it into the net.

The second set rumbled on with serve until 4-4 when Riske conjured up a powerful return which smacked the baseline followed by a delicate volley, before holding to love and levelling the match.

Breaks were exchanged again twice at the start of the decider, the Americans now matching each other blow for blow until a stunning Williams volley and a Riske double-fault broke the 29-year-old once more.

Serving for the match after two hours and one minute, Williams fired down an 18th ace to pass her toughest test yet and reach the last four.