MELBOURNE- American Madison Keys relied on her big serve on key points to outclass 2020 Australian Open champion Sofia Kenin 7-6(2) 7-5 on John Cain Arena on Monday and reach the second round of the year's first Grand Slam.

Former U.S. Open runner-up Keys, who won her first trophy since 2019 at the Adelaide International 2 warm-up event last week, struggled to gain the upper hand in the contest before sealing the opening set in a tiebreak with her eighth ace.

"My serve was helping out a lot today, being able to close that out, to start on the front foot and to not have to work my way back into the match was really helpful," Keys, who finished with 15 aces, told reporters.

"I feel I've really found my rhythm with that, it really helped me close out the first and second set in big moments. I'm going to make sure it's ready for the second round."

In a see-sawing second set, Kenin conceded a decisive break to allow her fellow American to go ahead 6-5, and although the 23-year-old saved two match-points, she was unable to prevent Keys closing out the victory on serve.

Kenin has won her only Grand Slam title at Melbourne Park and has otherwise struggled to raise her game at majors, losing to Keys in straight sets in their last encounter at the U.S. Open three years ago.

"At this point every first round is tough, but when you have to go up against a Grand Slam champion it's never easy," said Keys, who reached the 2015 semi-finals at Melbourne Park.

Keys faces Jaqueline Cristian next, after the Romanian beat compatriot Greet Minnen 7-5 6-4.

(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Pravin Char and Christian Radnedge) ((;))