Resilient Keys beats Svitolina to reach Australian Open semi-finals
The American 19th seed moved into the last four at Melbourne Park for the third time, 10 years after her first, where she will meet either Iga Swiatek or Emma Navarro for a place in the final.
Keys, who will be 30 next month, leads the WTA Tour with 12 wins this season and is now on a 10-match unbeaten streak after lifting the Adelaide title.
She had to show her resilience to fight back against Svitolina, who held the upper hand in the early stages.
"I felt like I kind of just had to start playing a little bit more aggressive and try to get to the net a little bit quicker," admitted Keys, who had battled past former Melbourne finalists Elena Rybakina and Danielle Collins on her way to the last eight.
"She was, you know, controlling a lot of the points and making me run.
"So I felt like I needed to try to get the advantage a little bit quicker.
"And luckily, I was able to do that," added Keys, who beat world number six Jessica Pegula in the Adelaide final and will now move back into the top 10 in the rankings.
The first set began in cagey fashion until the eighth game, when Svitolina converted her first break point as Keys went long to take a 5-3 lead.
She created three set points with an ace out wide and then sealed the opener in 33 minutes when Keys netted.
Keys, who was playing defensively in the first set, upped her pace at the start of the second.
The American created three break points in the fourth game but Svitolina negotiated them safely, the third via a lightning reflex volley at the net.
Keys was not to be denied, creating two more openings at 3-2, securing the second with a forehand winner from the baseline and serving out to level the match after 76 minutes.
With only a single dropped serve each, the next break was likely to be the pivotal one.
Keys created two more chances to break at 2-2, jumping all over the second of them with a backhand return winner to move ahead.
The winners kept flowing and she sealed her place in the last four in 1hr 53min.