Ajla Tomljanovic's staggering act to set up Serena Williams showdown

Ajla Tomljanovic has staged an incredible comeback to win her second-round clash at the US Open and set up a blockbuster showdown with Serena Williams.

The Aussie star lost the first set badly and was down a service break deep in the deciding set before coming back to beat Evgeniya Rodina 1-6 6-2 7-5 in an intense slugfest on Wednesday night.

'DISGRACE': Kyrgios' girlfriend caught in ugly controversy at US Open

UGLY: Jordan Thompson in mid-match altercation with opponent

The two-time Wimbledon quarter-finalist will now face Williams in the third round after the 23-time grand slam champion shocked World No.2 Anett Kontaveit 7-6 (7-4) 2-6 6-2 just minutes later.

"Yeah, it's definitely something I'll never forget in my career. Definitely be something I have never experienced yet," Tomljanovic said.

"It's going to be a huge moment no matter the outcome. But no matter the fact that I've been a Serena fan since I was a kid, on Friday night I'll just be a competitor and I'll try my best to win."

Williams eliminated the second seed to ensure she will play at least one more singles match before her impending retirement.

Tomljanovic feels it's a touch of fate that she finally gets to play the 23-time grand slam champion.

"I don't look at the draws, so I wasn't sure where she was but I did have a moment of, like, before the tournament started when I was in my bed and just thought about playing her here on Arthur Ashe before the draw came out," said the Aussie No.1.

"I'm glad that it's now in a third round.

"It's a little surreal to me that I made it and played in the same era as her, but I was quite sad before this tournament that I've never faced her so far. Could have been a chance I'll never play her before she retires."

The 40-year-old Williams was again buoyed by a loud crowd at a packed Arthur Ashe Stadium on Wednesday night, just as she was in the first round two days earlier.

She hit serves at up to 190 km/h, stayed with Kontaveit during lengthy exchanges of big swings from the baselines and conjured up some of her trademark brilliance when it was needed most.

After pulling out a tight first set, then faltering a bit in the second, Williams headed to the locker room for a bit of a break before the third.

When they resumed, it was Williams who lifted her level and emerged as the better player - just as she's done so many times on so many stages, with so much at stake.

Serena Williams sends tennis world into meltdown

In staggering scenes, Williams once again seemed to suggest the US Open might not be her farewell tournament after all.

“I’m not in any rush here (to leave),” Williams said in her on-court interview.

“I’m loving this crowd, and there’s still a little left in me. We’ll see.

“This is what I do best, I haven’t played many matches but I have been practicing really well.

“The last couple of matches in New York it’s really come together.”

When asked about the remarkable win, Williams said: “I’m just Serena, you know?

“I’m just looking at it as a bonus, I have nothing to prove ... I have nothing to lose.

“I haven’t been able to play like this since 1998, I’ve had an X on my back since 1999.

“I’m a pretty good player, this is what I do best and I love rising to the challenge. I don’t have anything to lose, anything to prove. It is kind of fun.

“When I step out on the court, I just want to do the best that I can do on that particular day.

“It’s been such a hard decision (retirement). I think when you’re passionate about something and love something so much, it’s always hard to walk away. Sometimes I think it’s harder to walk away than not and that’s been the case for me.”

Third-seeded Greek Maria Sakkari had earlier become another big casualty in the women's draw, falling to a 3-6 7-5 7-5 defeat to unseeded Chinese Wang Xiyu in an absorbing second-round contest.

Sakkari, a semi-finalist in New York last year, took charge in the early stages of Wednesday's match and marched into a one-set lead before being let down by a series of unforced errors as Wang claimed her first career victory over a top-10 player.

Despite Sakkari's superior experience, Wang's heavy hitting from the baseline came to the fore in the second set as she took a 5-3 lead before clinching it following a double fault from Sakkari.

with AAP

Click here to sign up to our newsletter for all the latest and breaking stories from Australia and around the world.