Swiatek has not won a Grand Slam since Wimbledon and has yet to win a title this year.
She lost in the third round of the French Open – the major she has won four times – and suffered a three-set defeat in her sole grass-court match in the build-up to Wimbledon.
Swiatek picked up where she left off on Centre Court, dropping just one game in a rapid first set and hitting 10 winners on the way.
However, her serve badly misfired in the second set – helped by Townsend standing inside the baseline to rush her – and she double-faulted to go a double break down.
Townsend has not won a singles match at Wimbledon since 2019 but she and Katerina Siniakova won the women’s doubles title together two years ago, and her superb touch and slice helped her level the match.
Swiatek went off court after a second set that saw her commit 16 unforced errors, but it took time to find her rhythm on her return.
A 12-minute first game of the deciding set was key, with Swiatek saving four break points and overcoming three double faults to hold serve.
Townsend – watched on by Siniakova and good friend Naomi Osaka – kept in touch but Swiatek broke for a 5-2 lead with a passing forehand, before serving out victory.
“You can see the relief on Iga’s face. It was a very intense match,” former Wimbledon champion Marion Bartoli said on BBC 5 Live.
“The moment it turned was in the very first game of the third set. It was absolutely pivotal because she was really losing the momentum of this match.
Swiatek will face Czech Karolina Pliskova, runner-up at Wimbledon in 2021, in the second round.
American Anisimova beat Macedonian qualifier Lina Gjorcheska 6-3 6-2 to advance, while 2024 finalist Jasmine Paolini fought back to beat Robin Montgomery 0-6 6-4 7-5.
