Australian Open 2019: Ninth seed John Isner toppled in battle of the giants

The 6ft 10in (2.08m) John Isner was beaten by 6ft 11in (2.11m) fellow American Reilly Opelka 7-6 (7/4), 7-6 (8/6), 6-7 (4/7), 7-6 (7/5) in a battle of the giants.

American number one and ninth seed John Isner was knocked out of the Australian Open on Monday in one of the biggest shocks of the first round.

United States' John Isner reacts during his first round match against compatriot Reilly Opelka at the Australian Open. (AP)

The 6ft 10in (2.08m) Isner was beaten by 6ft 11in (2.11m) fellow American Reilly Opelka 7-6 (7/4), 7-6 (8/6), 6-7 (4/7), 7-6 (7/5) in a battle of the giants.

No fewer than 87 aces were powered down between the big-serving pair with just one break apiece being registered in the fourth set of a match that lasted 2hr 58min.

Isner, 33, had not lost a Grand Slam match to a player ranked as low as number 97 Opelka, who is 12 years his junior, since retiring due to a foot injury while trailing 106th-ranked Martin Klizan in the first round at Melbourne in 2014.

Opelka has never before reached the second round of a Slam and will next face Italy’s world number 102 Thomas Fabbiano, who beat Australian wildcard Jason Kubler 6-4, 7-6 (7/1), 2-6, 6-3.