Teenage sensation Joao Fonseca announced himself on the big stage by knocking out ninth seed Andrey Rublev in the first round of the Australian Open.

The 18-year-old Brazilian is the hottest young property in men’s tennis after winning the Next Gen ATP Finals for the best players aged 21 and under last month and then qualifying for the main draw of a grand slam for the first time here.

Given a prominent draw against a player who has made the quarter-finals in three out of the last four years, Fonseca rose to the occasion superbly to claim a 7-6 (1) 6-3 7-6 (5) victory.

Russia’s Andrey Rublev throws his racquet during his first round defeat to Brazil’s Joao Fonseca. Photo: Reuters/Jaimi Joy

Holger Rune also needed five sets to make it past China’s Zhang Zhizhen while another match that went the distance saw veteran Gael Monfils win the battle of the Frenchmen against his young compatriot Giovanni Mpetshi Perricard.

Like Fonseca, 21-year-old Mpetshi Perricard is one of the top prospects on tour and he sent down by some distance the fastest serve of the tournament so far at 144.2 miles per hour but 38-year-old Monfils, who became the oldest winner of an ATP Tour singles title in Auckland at the weekend, triumphed 7-6 (7) 6-3 6-7 (6) 6-7 (5) 6-4.

“I don’t really look up my age,” Monfils said. “It is just a number. Then I try to avoid to think about it, but I can tell you that tomorrow morning I will be more 48 than 38.”

Fourth seed Taylor Fritz had a much easier time of it, breezing past fellow American Jenson Brooksby 6-2 6-0 6-3, while home hero Alex De Minaur defeated Botic van de Zandschulp 6-1 7-5 6-4.

Dutchman Van de Zandschulp may well have hit the shot of the tournament, though, with a through-the-legs winner that left De Minaur applauding.

In the women’s competition, Emma Raducanu joked her serve had “a mind of its own” after she battled her way to victory over 26th seed Ekaterina Alexandrova despite 15 double faults.

Nine of them came in the first five games and several at key moments, but the issue did not prevent Raducanu claiming her best win at the Australian Open, clinching a 7-6 (4) 7-6 (2) victory after two hours and 16 minutes.

The 22-year-old has been working to improve her serve with coach Nick Cavaday, but it is certainly not the finished article.

“I’m not sure what I changed in my serve today,” she said. “I think it had a mind of its own. I will be sure to reflect, look at that and come back to you.

“I think in the first set I was hitting a lot of good first serves. I hit a few aces. At the same time, I was hitting a double fault. I was quite accepting of that: ‘OK, I’m at least going for it’.”

She continued: “I think, as the balls got heavier, it was a lot more difficult. More kept coming, it was not easy to refocus, but I knew that, even if I was down, I have great returns. It was good to be able to rely on other parts of my game today that I know are quite strong, as well.

“I’m just very proud that I didn’t let it affect me too much and let the match run away from me.”

Raducanu is hopeful it will be better in her second-round match against another former teenage prodigy, American Amanda Anisimova, on Thursday.

“I’ve had experience having teething problems with it and then being able to come back and fix it for the next match,” she said. “I’m looking forward to getting back out on the court tomorrow and working on it.”

Raducanu’s enduring popularity was evidenced by big queues outside Court 3 as the match began under a cloudless Melbourne sky.

Alexandrova, a big ball striker with a relentlessly negative demeanour, experienced her own difficulties on serve and there were eight breaks in the opening set.

Raducanu again showed her X factor on returns, twice breaking Alexandrova when she served for it, while she won just her third of 17 second serve points at 4-4 in the tie-break before arrowing a forehand into the corner to clinch it.

The British number two was the better player for most of the second set but the service problems resurfaced after a steadier start and she had to save a set point at 5-6.

Having forced another tie-break, Raducanu was almost flawless, with one final double fault the only blemish.

Raducanu came into the season feeling the effects of a back spasm that prompted her to pull out of her planned opening tournament in Auckland, while she missed two months late last year with a foot injury, so this was a good physical test.

“I think it was quite a long match,” she said. “First match of the season. I haven’t necessarily played outdoors for a long time, since Seoul (in September).

“I think for me playing two sets was good but, equally, I felt pretty fit out there. Right now I feel good in my body. I think it’s just a testament to the work I’m starting to do off the court. I didn’t necessarily feel any restrictions.”