World number one Halep had needed three sets in each of her opening two matches in Melbourne, but was in commanding form during a 6-2 6-3 rout of Williams on Margaret Court Arena.

The Romanian's questionable reward is an encounter against 23-time grand slam winner Serena, who she has not faced since the 2016 US Open.

More of the aggression and variety she showed here against Venus will be needed, but Halep can take plenty of confidence from a dominant performance

Halep was the aggressor from the off and a couple of break points had already gone begging by the time she made the breakthrough in game five by working the angles and finishing with a clinical double-backhand winner.

Perhaps roused by falling behind, Williams had Halep on the ropes with four break points in the next game, but the Romanian staved off the threat - saving the last with a wonderful deft drop-shot.

The writing was on the wall for the first set when Williams went long to cede a double break and things worsened when Halep broke again at the start of the second.

Williams hit straight back, though, and - after saving a couple more break points in game three - she was holding her own in the set until Halep's counterpunching paid dividends for a big break to lead 4-3.

There was no way back from there and Halep sealed the win with a crunching forehand, which will need to be firing on all cylinders against Serena.