World number one Simona Halep survived a stern test in the second round of the Australian Open as she overcame Sofia Kenin 6-3 6-7 (5-7) 6-4.

Halep, who split with coach Darren Cahill at the end of last season, came from a break down in the final set to book a third-round clash with Venus Williams.

It is just the fifth time in the Romanian's career that she has progressed beyond the second round in Melbourne.

Halep, who was limited to one competitive match in the lead up to the year's first grand slam, quickly broke for a 1-0 lead before Kenin finally settled, but the world number 37 – the 2015 US Open girls' singles runner-up – was unable to find a way back into the first set.

Halep looked comfortable as Kenin tried to match her from the baseline and the French Open champion broke to 15 for a 2-0 lead in the second set.

But Kenin broke back in the fifth game, a ripping backhand winner down the line seeing her convert a rare opportunity.

The American started to hold her own from the back of the court and got to a tie-break, a backhand winner and Halep error from 5-5 bringing the match level.

The 20-year-old carried that confidence into the deciding set and found herself a break up when Halep sent a backhand long for 4-2.

But Halep showed her resolve to break back immediately and made it four games in a row to clinch a victory that had looked in serious doubt.

"I have no idea how I won tonight," conceded Halep after the match, also revealing she got "a little bit injured" in the second set.

STATISTICAL BREAKDOWN
Halep [1] bt Kenin

WINNERS/UNFORCED ERRORS
Halep - 33
Kenin - 32

ACES/DOUBLE FAULTS
Halep - 9
Kenin - 1

BREAK POINTS WON
Halep - 5/14
Kenin - 2/4

FIRST SERVE PERCENTAGE
Halep - 63
Kenin - 71

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Halep - 75/55
Kenin - 58/55

TOTAL POINTS
Halep - 115
Kenin - 103