Chris O'Connell is visibly annoyed by a poor call from an umpire, but regathered himself to claim a stunning five-set victory.

Meanwhile, Novak Djokovic's four-hour epic against an 18-year-old Croatian ensured that there would be another late start to a match at Melbourne Park, but Aryna Sabalenka made sure it wouldn't be a late finish with a brutal display that left her own 18-year-old opponent in tears.

Here are five quick hits from day one at Melbourne Park.

1. O'Connell dudded by bad call

With automatic line calling in place for the Australian Open, chair umpires don't really have that much to do.

But in Chris O'Connell's first round match against Cristian Garin, the umpire inserted herself into the action with a demonstrably bad call to throw the Aussie off his game.

With the match evenly poised at 1-1 but O'Connell trailing 1-2 in the third set, the Australian raced forward and looked to have scooped a drop shot just up and over the net in the fourth game.

However, umpire Ana Carvalho of Brazil said that O'Connell had not got there in time and the ball bounced twice.

The replays clearly showed that O'Connell made it on time, right under the umpire's chair.

O'Connell was upset, arguing his case as the crowd made its thoughts clear by booing.

However, even with the replay clearly showing that the Australian was in the right, the call stood and the score stood at 30-30.

There was no guarantee that O'Connell would have won the point — Garin was closing fast — but that he didn't even have to make the shot could have been telling, especially as the Chilean ended up winning the game.

2. The late, late show

Starting on a Sunday, making the Australian Open a 15-day tournament for the first time, was expressly to avoid the sort of late finishes that have blighted the competition in the recent past.