Swiss teenager Bencic took it to Williams but the former world number one survived to triumph 6-4 6-3 in sweltering conditions at Melbourne Park.

Williams - runner-up at the tournament last year - did not have it all her own way, tallying 30 unforced errors and four double faults on Rod Laver Arena.

The 22-time grand-slam champion, however, overcame her opponent to earn a second-round showdown with Lucie Safarova.

"I think it was pretty good. I mean, she's a really good player," Williams told reporters of her performance.

"I think I was able to start out well."

After taking out the opening set, Williams was cruising at 5-0 in the second, with a second-round berth all but secured.

But Bencic had other ideas as she reeled off three consecutive games to force her way back into the contest.

Williams then double-faulted twice in her attempts to serve for the match again, though she was not to be denied after an hour, 19 minutes.

"I just wasn't as aggressive as I was during those games. You know, she started playing better," the 35-year-old American added.

"I made a few errors on some key points, but for the most part, I still was going for everything and I was able to close it out."