The 21-year-old ended Isner’s nine-match unbeaten Grand Slam record against American opposition after two hours and 58 minutes, firing 40 aces to record his first Grand Slam victory. Isner also landed 47 aces in a match which featured a combined 143 winners.
Opelka’s only previous Grand Slam appearance came as a qualifier in Melbourne, falling in five sets to David Goffin in 2017. The World No. 102 improves to 2-1 against Top 10 players, having also beat then-No. 8 Jack Sock at 2018 Delray Beach.
Grigor Dimitrov recovered from a set down to beat Janko Tipsarevic 4-6, 6-3, 6-1, 6-4. The 2017 semi-finalist (l. to Nadal), making his ninth straight appearance at Melbourne Park, fired 42 winners, including 18 aces, to advance after two hours and 33 minutes.
During the off-season, Dimitrov has continued to work with former World No. 1 Andre Agassi in Las Vegas. Agassi began work with the 2017 Nitto ATP Finals champion at the Rolex Paris Masters last November, as Dimitrov looks to make a return to the Top 10 in the ATP Rankings.
“[Andre has] done so much outside of the court,” said Dimitrov. “I’m just a better person, period. On a daily basis, I have learned something new from him.”
McEnroe Weighs In On Agassi-Dimitrov Partnership
The 20th seed, who entered the match with a 1-4 FedEx ATP Head2Head record against Tipsarevic, improves to 3-1 this season after a run to the Brisbane International quarter-finals (l. to Nishikori). Former No. 8 Tipsarevic was making his first appearance at any level since the 2017 US Open, following surgery on both hamstring tendons.