An emotional Serena Williams warned her rivals "this is just the beginning" after she thundered into the US Open final on a stormy evening in New York.

Williams is one win away from equalling Margaret Court's record of 24 grand slam singles titles, having crushed Anastasija Sevastova 6-3 6-0 in Thursday's first semifinal at Flushing Meadows.

A year on from suffering severe complications following the birth of her first child, Serena looks back to her brilliant best and will undoubtedly start as the favorite against Madison Keys or Naomi Osaka in the final.

The veteran American lost in the last four here in 2015 and 2016, but will now get her chance to claim a seventh title on Arthur Ashe Stadium, an incredible 19 years after her first triumph at the venue.

"It's honestly really incredible [to be back in the final at Flushing Meadows]," said Williams in an on-court interview with ESPN following her win over Sevastova.

"A year ago I was fighting literally for my life at the hospital after having my baby. Every time I step out on the court I am so grateful I have this opportunity. No matter what happens ... I feel I've already won."

"To come this far so fast [is amazing] ... and I'm just beginning, you guys, this has only been a few months. I'm really looking forward to the rest of the year and next year. This is just the beginning."

Sevastova is renowned for her use of drop shots, but found herself overwhelmed as Williams came forward at every opportunity, winning 24 out of 28 points at the net.

"I've been working hard on my volleys. I have won a few doubles championships, so I know how to volley," added the 36-year-old with a laugh.

"I usually come in only to shake hands, but tonight I knew if I wanted to have a chance against Anastasija, I'd have to come in."

"I wanted to try something different today and it worked in my favor."