Venus Williams defied her physical problems to beat Italy's Camila Giorgi in an emotional first-round thriller at the Birmingham Classic.
American Williams appeared to be in tears after taking a medical timeout just five games into the match.
However, with her right knee heavily strapped, the 43-year-old battled to a 7-6 (7-5) 4-6 7-6 (8-6) win.
It was only Williams' second singles victory in almost two years after lengthy injury lay-offs.
"I hit some 120mph serves and I haven't done that in a couple of years - I was like, I've missed you!" Williams, now ranked 657, said.
"I thought I played well today and she did too. I'm surprised she's not number one in the world.
"There were so many moments where I thought the match was over and she hit a shot out of nowhere so she pushed me to be better than what I thought I could be."
Williams, a seven-time Grand Slam singles champion, received vocal support from the Birmingham crowd as she pushed through her physical limitations in a gruelling encounter.
She had lost on her return to grass-court tennis at the Libema Open last week but, despite a heavily strapped right knee, showed some of her trademark grit to secure victory over Giorgi.
"I got out to a great start and my leg started hurting in the third game and I thought 'oh no not this'", Williams added.
"It was hard to control my emotions. Eventually I just tried to ignore it - I couldn't move as well as I wanted but I tried to get to every ball."
Williams battles past Giorgi in engrossing match
In an intriguing start, former world number one Williams secured an early double break in the first set but was left close to tears after taking a medical timeout.
Giorgi sought to capitalise but the five-time Wimbledon singles champion saved break point with back-to-back aces, despite the heavy strapping on her knee and some lethargy between points.
World number 48 Giorgi reeled off the next three games but Williams held firm to force a tie-break, which she claimed with a stunning backhand winner.
Williams looked zapped of energy in the second set, falling a double-break down but rallying remarkably to break back before Giorgi's powerful hitting forced a deciding set.
Although she is entering the latter stages of her career, Williams, who accepted a wildcard to compete in Birmingham, showed little sign of relenting in the third.
She secured yet another early break before Giorgi rallied from 5-2 down to force a tie-break without facing a single match point.
But Williams was patient and showcased her experience to see out her first victory over a top-50 player since 2019 and set up a last-16 tie against the Czech Republic's Linda Noskova or Latvian second seed Jelena Ostapenko.
Earlier, Ukrainian Elina Svitolina was dismantled 6-2 6-0 in just 52 minutes by Czech 18-year-old Linda Fruhvirtova.
Following an impressive run to the French Open quarter-finals, Svitolina slumped to a 4-0 deficit and had no answer to the teenager's dominance in the second set.
It marks Fruhvirtova's first win in five matches and she will face American Bernarda Pera in the last 16, having never played a main-draw WTA match on grass before Monday.
At the German Open, two-time Wimbledon winner Petra Kvitova sealed a 6-3 6-4 opening-round victory over compatriot Karolina Pliskova, her first victory since triumphing at the Miami Open in April.
France's world number four Caroline Garcia overcame German wildcard Sabine Lisicki 7-6 (7-2) 6-3 to reach the last 16.