Kasatkina wins break filled first set in tiebreak to take the lead
In a stunning beginning, it was Kasatkina who raced out to an immediate and commanding lead, winning the first eight points of the match to go ahead 2-0. Her lead would expand to 4-1 after breaks were traded and the Russian held.
Kerber fought back and she broke back in a marathon seventh game. The German again faced a challenge, needing to save a set point in the ninth game and from there, both players held to send the opening set to a tiebreak.
The first five points of the tiebreaker went to the server before Kasatkina secured the first minibreak to go ahead 4-2. Kerber again rescued her deficit to level at 5-5. The next point would be the decisive one as Kasatkina again gained a minibreak, but this time the Russian won the following point on her serve to close out the set.
Kasatkina runs away with second set to reach final eight
Buoyed by her opening set success, Kasatkina again grabbed the initiative with a quick break to put herself in a strong position. Kerber was able to fight back and tie up the set at 2-2. Little did she know that would be her last game of the match.
Kasatkina scrapped and dug out a break that would put her ahead for good. After saving three break points in a 12-point game, the Russian glided to the finish, breaking again for a 5-2 lead. The 20-year old stepped up and served out the match in commanding fashion, setting up a quarterfinal match with Johanna Konta.
Kasatkina speaks about her victory
"First, my thought was, finally, I won on match point, because I lost a few good matches from the match point last year and this year already," Kasatkina said. "For me, it was important. This match was very important for me. I was three matches from match point against Top 10 players, and today I beat No.1 in the world. So I think I am somewhere close [to her level]."
Kerber reacts to surprise defeat
"The first matches of the year are always tough, and I'm still not feeling my rhythm. I made too many mistakes. I was not feeling the ball. It's tough, but I think it was still good to have a match before going to Melbourne."