MELBOURNE, Australia - For the fourth time in the past five years, Madison Keys is back in the second week of the Australian Open.

The American No.17 seed delivered a punishing performance to oust No.14 seed and 2018 semifinalist Elise Mertens of Belgium on Friday in Melbourne to return to the round of 16, 6-3, 6-2.

Beginning with the 2015 semifinals, Keys has reached the fourth round or better in all of her appearances Down Under, with the only blemish being a pre-tournament withdrawal due to injury in 2017. 

Keys hammered 31 winners to just 21 unforced errors in the match overall, more than doubling Mertens' total of winners for the match.

The American lost serve just once - a near-perfect performance at the line which saw her save all seven break points she faced in the first set - and won four of Mertens' eight service games overall.

Winning a seven-deuce third game in the first set, in which she saved three break points, set the tone for the American in the match, and she immediately broke Mertens following that battle to take a lead she'd never relinquish. 

The Belgian had three more chances to get back on serve in the seventh game and one final opportunity in the ninth, but the American snuffed out each chance with big serving and bigger hitting off the ground to take a one-set lead on her third set point.

The second set began similarly for the 2017 US Open finalist, as a 0-40 lead in the first game turned into her first break of the second set.

Though she surrendered her serve for the first time in the match in the ensuing game and saw the No.14 seed take her first lead of the match behind her fourth hold of the match, Keys would not lose another game from there on out. 

"I think I played really well," the American said. "I served well, especially in the first set, getting out of some breakpoint situations. She played really well, which just made me raise my level.

"In the second set, being able to break a couple of times and bounce back from being broken back, overall I'm just really happy with how everything went today.

"It's definitely shaping up to be a very interesting first Grand Slam of the year. Everyone is just playing really well. Even the upsets aren't really upsets. Everyone is just playing really good tennis."