Australia's Sam Groth touches his racquet to his face as he reacts after missing a shot during his second round match against Britain's Andy Murray at the Australian Open tennis tournament at Melbourne Park, Australia, Jan 21, 2016. [Photo/Agencies]

It's the second time in three days that a major medical disturbance has occurred in the crowd, after a woman suffered an apparent seizure during Australian Bernard Tomic's first-round match on Tuesday.

Following Ivanovic's comfortable win, 3rd-seed Garbine Muguruza snuck past Belgian Kirsten Flipkens in an error-riddled 6-4, 6-2 victory.

Across on Margaret Court Arena, Frenchmen Gael Monfils and Nicholas Mahut went toe-to-toe, with the explosive Monfils packing too much power for his fellow countryman to win 7-5, 6-4, 6-1.

Before play got underway, Australian tennis legend John Newcombe, winner of seven Grand Slam titles, turned heads when he selected 13th-seed Milos Raonic to win the men's title.

But the young Canadian swiftly validated Newcombe's selection, going about his business with minimum fuss and effort by posting a 7-6 (8-6), 7-6 (7-5), 7-5 win over Spanish stalwart Tommy Robredo.

Another lowly-seeded dark horse in the women's draw, Victoria Azarenka, also progressed without great fanfare, despite another impressive performance in the second round.

The duel Australian Open-winner backed up her first-round 'double-bagel' - 6-0, 6-0 - with a 6-1, 6-2 sweep of Danka Kovinic of Montenegro, meaning she has only dropped three games through her first two matches.

"I really don't count the games," Azarenka said.

"I just enjoy myself on the court and try to play every point like it's my last point."

The 16th-seeded Bulgarian will play Elina Svitolina for a place in the fourth round, where she will likely meet Muguruza in a great test of both players' title credentials.

In other results, big-serving American John Isner negotiated his way through two tiebreakers to beat Spaniard Marcel Granollers 6-3, 7-6 (8-6), 7-6 (7-2), while Madison Keys survived a scare against Yaroslava Shvedova winning in three sets.

Weatherwise, Day 4 took a queue from its predecessor, with misty rain delaying proceedings on all outside courts at Melbourne Park once again.