Serena Williams made a solid start to her campaign for an eighth Wimbledon singles title with a 6-2 7-5 victory over Giulia Gatto-Monticone.
The 23-time Grand Slam champion had played in just five tournaments this year coming into Wimbledon, and showed signs of rust as she was broken attempting to serve out both sets.
However, she responded with an immediate break to take the first, and swiftly hit back in the second to seal victory in an hour and 20 minutes.
Despite the defeat, the match was a triumph of sorts for the 31-year-old Gatto-Monticone, who was playing in the Wimbledon main draw for the first time in her career.
The Italian produced a game performance, but was often unable to cope with the power of Williams, who struck 27 winners to her opponent's 11.
Williams will face another qualifier in the second round, after Slovenian Kaja Juvan defeated Kristyna Pliskova in three sets.
Ashleigh Barty appeared comfortable with her new status as world number one as she eased to a 6-4 6-2 victory over China's Saisai Zheng.
Barty, who is attempting to pull off a French Open-Wimbledon double, produced a typically solid display to extend her winning streak to 13 matches.
The Australian followed up her Roland Garros triumph by winning a grass court warm-up event in Birmingham last month to secure the top ranking.
"I think for me it's a little bit irrelevant," Barty said of her ranking. "The only pressure I have is what I put on myself, making sure I'm doing all the right things, preparing in the right way."
Also through to the second round is reigning champion Angelique Kerber, who beat fellow German Tatjana Maria 6-4 6-3 as she opened proceedings on Centre Court.
Despite being broken four times in the match, Kerber maintained her composure to break her opponent's serve on seven occasions.
Kerber beat Serena Williams in last year's final to claim her first Wimbledon title, and has been soaking up the experience of returning to the All England Club as champion.
"It is a huge experience for me," Kerber said. "Coming back as the defending champion, to see the names on the wall, like my name on the wall, the pictures, to have the opportunity to see it."
Another former champion, Petra Kvitova, joined Kerber in the second round with a comfortable 6-4 6-2 victory over Tunisian Ons Jabeur.
Kvitova, whose two Grand Slam titles came at Wimbledon in 2011 and 2014, is trying to win her first major since returning from the hand injury she suffered in an attack at her home in the Czech Republic in December 2016.
She came into the tournament with concerns over a left forearm injury that forced her to miss the French Open, but showed no signs of the ailment as she broke her opponent five times on the way to victory.
It was a far less happy return to the All England Club for 2017 champion Garbine Muguruza, as she lost 6-4 6-4 to unseeded Brazilian Beatriz Haddad Maia.
The Spaniard has now failed to go beyond the last 16 at six of her last seven major appearances, including a second-round exit at last year's Wimbledon.
Maria Sharapova is also out after retiring with injury while trailing 4-6 7-6 (7-4) 5-0 to Pauline Parmentier.
The 2004 champion required treatment on a left arm injury after giving up a 5-2 lead in the second set, and never appeared to recover as Parmentier raced ahead in the decider.
Elsewhere, ninth seed Sloane Stephens advanced with a convincing 6-2 6-4 victory over Timea Bacsinszky.
The victory ended a run of two straight first-round exits at the All England Club for the 2017 US Open champion.