The 18-year-old Canadian, whose rise to 50th in the ATP rankings in the past 12 months has been meteoric, won 6-1 6-3 7-6(5) against the 19-year-old he also beat on his way to claiming the Wimbledon junior title in 2016.
Shapovalov's colourful game, including a dreamy single-handed backhand, would look spectacular in any choice of kit, although the garish pink and black strip he wore made sure there was no mistaking him on a blustery Court Two.
Tsitsipas, who broke into the top 100 last year and reached the quarter-finals at the Qatar Open, could make little impression in the opening two sets but pushed Shapovalov hard in the third, breaking back to take it into a tiebreak.
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Shapovalov crunched away a smash on his first match point though to set up a likely second-round clash with Frenchman Jo-Wilfried Tsonga, who was in action later on Monday.
Shapovalov's first year on the circuit began last season began in ignominious circumstances when he was defaulted in a Davis Cup title against Britain's Kyle Edmund after slamming a ball in frustration and hitting the chair umpire in the eye.
The Israel-born teenager has rebounded in style, however.
He reached the semi-finals of the Montreal Masters, beating world number one Rafael Nadal, before winning his first grand slam match at the U.S. Open, where he made round four.
One of a bunch of fast-rising young guns looking to make their mark in Melbourne, Shapovalov said he expected many more battles with Tsitsipas in the future.
"I'm going to win some and lose some," he told reporters. "I managed to play better today. Maybe I have a little more experience after my run at the U.S. Open and definitely today I felt comfortable, whereas he looked a bit tight early on.
"I definitely feel I'm on top of my game."
(Reporting by Martyn Herman; Editing by John O'Brien)
