Serena Williams moved one match closer to making more tennis history at the Australian Open, but her bigger struggle might be just getting out of bed.

Coughing, spluttering and croaking, she gutted out her best win of the tournament by dominating 2014 finalist Dominika Cibulkova from start to finish, winning their quarter-final 6-2, 6-2. Her intensity was no doubt informed by the debilitating effects of the virus that has been with her for most of the fortnight.

Barely able to talk, she said in her courtside interview: “I’m just happy to come through. I don’t have anything to lose.”

She did all her talking on the court, serving like the wind, the fastest of her 15 aces flying past Cibulkova at 200kph, and her ground strokes revived memories of Serena at her most dominant.

Cibulkova did not play badly; she was simply not allowed to play.

Five times Williams has reached the semi-finals here, and five times she has won the title. If she wins another one she will move to within three majors of Steff Graf's record Open era tally of 22 and, on this showing, she would start favourite – as long as she can get past fellow American Madison Keys, who beat her sister, Venus, 6-3, 4-6, 6-4 in the early quarter-final.

So young

“I didn’t watch Venus’s match,” Serena said. “I was just getting ready for my match. But it’s great [for Keys], not only so young, but African-American – and regardless there’ll be an American in the final.”

Keys has her own problems, however, leaving the court at 1-4 down in the second for treatment to a tight leg muscle.

“It was definitely a flashback to Wimbledon for me [when she had to quit during her rain-interrupted third-round match against Yaroslava Shvedova],” Keys said.

“I have had some problems with that part of my leg. It’s been tight [all tournament], but with some treatment it’s been fine. Then one shot in the match [a backhand in the fifth game] all of a sudden I felt it really get tight. I thought I was close to pulling it. I ignored it at Wimbledon and tore it, and ultimately had to withdraw.

“It was kind of a panic [here]. I need to get some tape on this so I don’t do that again. It was an overwhelming moment, kind of scary. But luckily I was able to catch it before I did any real damage.”

Fine form

For Venus, who lives with the daily prospect of her auto-immune disease striking without notice, she has been in fine form in Melbourne, but could not cope with Keys’s power when she hit her stride in the third set. Venus’s serve was off and she gave Keys too many opportunities to take centre court. “It already feels like a long season, so many matches in a row. But it’s a great start. Hopefully I’ll be able to keep this level up.”

For the other walking wounded, ailments are temporary. For Venus, a shadow stalks her every day. She was desperate to make this semi-final, mainly to be reunited on a big stage with her sister. Guardian service