The 18-year-old won 4-6 6-1 6-4 to reverse last week’s loss to world No.
9 Fish at the Japan Open.
The 49th-ranked Australian had only won one match previously against top 10 players, but levelled with two breaks in the second set and a single break in the ninth game of the decider to earn the win.
Tenth seed Andy Roddick refocused after losing his cool to post a 7-6 (7-3) 7-5 win over Bulgaria’s Grigor Dimitrov.
Roddick won a first set tie-break and sealed victory after clinching a topsy-turvy second set that contained five breaks of serve.
After Dimitrov broke Roddick in the ninth game of the second set to lead 5-4, the American smashed his bag repeatedly in frustration but immediately broke back to level at 5-5, saving a set point.
Speaking about the incident, Roddick said: “I don’t know that I made a first serve that game, so that was frustrating for me.
“So I was kind of pissed. I felt like I was getting it backwards a little bit.”
Also in second round action, Swiss 13th seed Stanislas Wawrinka beat America’s Donald Young 6-7 (5-7) 7-6 (7-2) 6-2 and France’s Gilles Simon, seeded eighth, eased past Spain’s Albert Montanes 6-1 6-1.
Earlier, Germany’s Florian Mayer, the 15th seed, beat former world No.3 David Nalbandian 6-3 6-4 to reach the third round and seventh seed Nicolas Almagro defeated Spanish compatriot Tommy Robredo 7-5 6-3.
In first round clashes, Serbian ninth seed Janko Tipsarevic crashed out to Feliciano Lopez of Spain 6-7 (2-7) 6-7 (3-7), dealing a heavy blow to his hopes of reaching the ATP World Tour Finals.
Tipsarevic won his first ATP title earlier this month at the Malaysian Open but lost in the first round of last week’s Japan Open.
Tipsarevic’s Serbian compatriot Viktor Troicki, seeded 11, also lost, beaten in straight sets by America’s Ryan Harrison.
Austrian 14th seed Jurgen Melzer, who defeated Rafael Nadal to reach the quarter-finals in Shanghai last year, beat Croatia’s Ivan Ljubicic and Alexandr Dolgopolov, seeded 12, beat Lukasz Kubot of Poland.
Japan’s Kei Nishikori overcame a disastrous start against Robin Haase to defeat the Dutchman 0-6 7-5 7-6 (7-5).