Defending men's champion Novak Djokovic and women's top seed Iga Swiatek started their Wimbledon campaigns in ominous fashion on Monday as rain temporarily halted play on the outside courts but expected climate protests failed to materialise.

Djokovic, 36, has only lost twice at Wimbledon in a decade and began the Centre Court programme with a 6-3 6-3 7-6(4) win over Argentine Pedro Cachin after a 70-minute delay despite the roof being closed as ground staff laboured to dry the turf.

The Serbian jokingly wiped the grass with a towel during a frustrating break in play before ground staff deployed leaf blowers to get the job done and allow Djokovic to get his quest for an eighth Wimbledon title off to flying start.

French Open champion Swiatek put down a marker on her least favourite surface as she powered past China's Zhu Lin 6-1 6-3, the contest finishing under the Court One roof due to rain.

World number one Swiatek, who last month claimed her third Roland Garros crown in four years and is eyeing a fifth Grand Slam title, meets Spain's Sara Sorribes Tormo next.

There were mixed fortunes for two highly-rated Americans on day one. Fourth seed Jessica Pegula advanced with a blustery 6-2 6-7(8) 6-3 win over fellow American Lauren Davis.

But 19-year-old seventh seed Coco Gauff's hopes were shattered as she lost 6-4 4-6 6-2 to compatriot Sofia Kenin, the former Australian Open champion who came through qualifying.

"This means a lot, I had to go through qualies," Kenin said. "I battled out there, and I took this match as any other match. I know Coco has had a great season, I'm super proud of myself."

FAMILIAR FACE

Earlier, the All England Club gates swung open for the start of the grasscourt major with some notable absentees but one very familiar face in Djokovic fixing his eyes on more records.

Wimbledon's favourite son Roger Federer, now retired, the injured Rafa Nadal and Serena Williams, also retired, are hard acts to follow and fans will lament their absence.

Australian maverick Nick Kyrgios, who pushed Djokovic hard in last year's men's final and whose spiky presence inevitably spices the fortnight, is also missing having pulled out with a wrist injury on the eve of the slam.

But Wimbledon remains rich in plots, not least Djokovic's quest to match Margaret Court's record 24 Grand Slams, equal Federer's eight Wimbledon crowns and move alongside the Swiss and Bjorn Borg's record of five successive titles.

The Serbian began in serene fashion, although he was as mystified as everyone else by the lengthy stoppage after light rain got onto the surface before the roof slid shut.

"It was very strange that for more than an hour the situation was not changing at all for the better," Djokovic told reporters. "Hopefully they'll fix (it) because if it starts raining, if you can't play under the roof, that's a little bit of an issue for schedule."

Five-time champion Venus Williams made her record 24th appearance in the women's singles, aged 43. But any hope of rolling back the years was ended by Ukraine's Elina Svitolina who won 6-4 6-3 in a high-profile battle of the wildcards.

EXCITED CROWDS

Wimbledon began with heightened security and longer-than-usual wait times in the famous queue outside the grounds because of the threat of climate change protests.

There was no repeat of events at Lord's last week when activists tried to throw orange powder on the pitch at the Ashes cricket test but fickle British weather caused more of a problem with several first-round matches not completed.

But there was still plenty for the capacity crowd to enjoy.

Italian eighth seed Jannik Sinner impressed as he trounced Argentina's Juan Manuel Cerundolo 6-2 6-2 6-2 while fourth seed Casper Ruud of Norway had a little more trouble, dropping a set on his way past French qualifier Laurent Lokoli.

Canada's 11th seed Felix Auger-Aliassime became the highest men's seed to fall though, suffering a shock 7-6(4) 6-7(4) 7-6(4) 6-4 defeat against American Michael Mmoh.

Andrey Rublev marked the return of Russian and Belarusian players after last year's ban following the invasion of Ukraine as the seventh seed beat Australian Max Purcell 6-3 7-5 6-4.

Seventeen Russian and Belarusian singles players have had to sign a "nationality waiver" pledging not to support President Vladimir Putin's regime and all are competing as neutrals, including men's third seed Daniil Medvedev.

"I feel really happy to be back, because in general I didn't play much Wimbledon or I was injured or (there) was (the) pandemic or then they ban us," Rublev told reporters.

"So, of course, really special and really happy to be back in London to play at one of the best tournaments."

Belarus's twice Grand Slam champion Victoria Azarenka marked her return by beating China's Yuan Yue 6-4 5-7 6-4.