Young Canadian Shapovalov showcased his exciting skills in an impressive straight-sets victory, while Rublev needed five sets to wear down Spanish slugger David Ferrer.
Shapovalov, the 50th-ranked left-hander, reeled off a 6-1, 6-3, 7-6 (7-5) victory over Stefanos Tsitsipas of Greece in just under two hours in his first appearance in Melbourne.
Widely seen as one of the up-and-coming stars in men’s tennis, the 18-year-old hammered 33 winners, backing up a strong service game.
The Canadian made his entrance on the big stage in August with a win over Rafael Nadal at home in Montréal, before a run to the US Open last 16.
Another of the so-called “NextGen” brigade, Russian Rublev overcame Spanish veteran Ferrer in five sets to advance to the next round.
Rublev, the 30th seed, won an attritional battle with the doughty back-courter before prevailing 7-5, 6-7 (6-8), 6-2, 6-7 (6-8), 6-2 in three hours and 50 minutes on an outside court to reach the second round for the second straight year.
Rublev, the top-ranked Russian, reached the US Open quarterfinals last year where he lost to eventual champion Nadal after upsetting Grigor Dimitrov on the way.
The 20-year-old claimed 13 service breaks and hit 77 winners, 40 of them coming off his strong forehand, but also committed 91 unforced errors.
It was a merited win for Rublev over Ferrer, who was an Australian Open semifinalist in 2013, the same year he lost to Nadal in the French Open final.