The 37-year-old ninth seed is now just one victory away, against U.S. compatriot Sloane Stephens, from playing for the U.S. Open title for the first time since 2002.
Keys, who missed the first two months of the season recovering from wrist surgery, is peaking at the right time and blazed into the her semi-final with a 69 minute 6-3 6-3 dismantling of Estonia's Kaia Kanepi. There are many more Grand Slams to come.
Unseeded Sloane Stephens held her nerve after an terrible second set to beat Venus Williams and reach her first Grand Slam final at the US Open.
"This feels really good", said Keys.
"I think I'm still gonna play the tournaments I planned before [the US Open]", Kanepi said, commenting on her plans for the near future.
"I played pretty well".
"I have no words to describe what I'm feeling, what it took to get there", she told the crowd in her on-court interview. Defending that constantly, I'm just going to really have to do everything really well.
Wimbledon champion Garbine Muguruza is assured of moving up to No. 1 in the WTA rankings for the first time, despite losing in the U.S. Open's fourth round.
The big-serving Czech had previously said that being number one came with additional pressure to perform at the tournament, where she lost in the final past year to Angelique Kerber. "The auto ride over, I was definitely feeling it".
Stephens beat Keys in the second round at Miami in 2015 in their only career meeting.
"There were definitely a lot of dark moments", Keys said. "But now she has a great team behind her and she is shining on the court". "I'm excited we get to play each other in the US Open final".
There have been comebacks aplenty with Sloane Stephens out 11 months after left foot surgery and Venus Williams back in the top five for the first time since 2011, the year she was diagnosed with the strength-sapping ailment Sjogren's Syndrome.
"I just worked my tail off and tried to run every ball down and here we are", Stephens said.
And with the victory Keys, now ranked No.16, is projected to rise to World No.12, and could move as high as No.9 with the US Open title.
However, she grew in confidence from clinging on and began to attack the Stephens serve at will, breaking three times to level without dropping a game. "I think my movement is probably what's kind of kept me in some of these matches, shockingly".
Williams finished with six double-faults and a total of 51 unforced errors, 24 more than Stephens.
Now she's playing in the US Open semi-finals.
The fourth seeded Indo-Chinese pair dispatched the fifth seed Hungarian-Czech combo 7-6 (5) 6-4 in the quarter-final which lasted one hour and 56 minutes.
As for the contest, Stephens made light of it being just her second Grand Slam semi-final and first since as a teenager she made the last four in Australia on 2013.
Sidelined for nearly a year after undergoing foot surgery, Stephens returned at Wimbledon and has been on a tear ever since, knocking off 11th seed Dominika Cibulkova, 30th seed Julia Goerges and 16th seed Anastasija Sevastova en route to the final four.