Djokovic's latest attempt to make history by winning a record 25th Grand Slam singles title got off to a rocky start as he laboured against unheralded Wu Yibing in the first round on Monday.The Serb knows he must raise his level when he returns to action against Stefanos Tsitsipas on Centre Court."I was really hanging on the ropes in the fourth. I probably should have lost that set to be honest," he said."I managed to fight and stay focused till the end. It's one of these matches that we have to dig deep."Bidding to become the oldest man to win a major title in the Open era, Djokovic -- who won the most recent of his seven Wimbledon crowns in 2022 -- has increasingly looked his age over the last two Grand Slams.The 39-year-old crashed out in the French Open third round, blowing a two-set lead against Joao Fonseca, after underwhelming displays in the first two rounds.But Djokovic can take heart from his dominance against world number 87 Tsitsipas.He has won their last 11 meetings, including the 2023 Australian Open final and the 2021 French Open final.Rattled by an unexpected bout of nerves and exposed by his lack of match action on grass this year, Sinner was fortunate to avoid becoming only the third defending men's champion to lose in the Wimbledon first round.Sinner was playing his first match since a shock second round loss against Juan Manuel Cerundolo at the French Open.The Italian world number one was in danger of another embarrassment after an awkward fall in the third set left him nursing a bloodied foot and a two-sets to one deficit.But, showing the spirit and stamina that helped him end Carlos Alcaraz's two-year reign as Wimbledon champion in 2025, Sinner scrambled out of trouble to book his Centre Court date against Portuguese world number 48 Nuno Borges.Serena Williams' Wimbledon comeback is in jeopardy after the American legend suffered a knee injury in her singles defeat to Maya Joint on Tuesday.Williams, a 23-time Grand Slam singles champion, is due to play in the doubles with sister Venus later this week on her comeback after four years in retirement.The 44-year-old's agent said Serena "is doing everything she can to be ready for her doubles match".'Just wanted to be here longer'Andreeva advanced from her previous Wimbledon showdown with Krejcikova in 2023 when the injured Czech withdrew after the Russian raced into 6-3, 4-0 lead.That was Andreeva's Wimbledon debut campaign as an unknown 16-year-old, while Krejcikova was just 12 months away from winning the All England Club crown for the first time with a surprise run that culminated in final victory over Jasmine Paolini.Fast forward three years and the roles are reversed.Andreeva, 19, is now tennis royalty after fulfilling her potential by winning her maiden Grand Slam title at the French Open recently.In contrast to the fifth seed's ascent, the 30-year-old Krejcikova has plummeted to 38th in the rankings after a dismal injury-plagued run including first-round losses at the Australian and French Opens this year.In Wednesday's early action, Japan's Naomi Osaka had a special motivation for her 6-3, 6-2 win over Russian Anastasia Gasanova."Tomorrow is my daughter's birthday and I just wanted to be here for longer," the 14th seed said."I didn't want to make her get on a plane on her birthday so I was really happy with today."The four-time Grand Slam champion will meet Janice Tjen or Daria Kasatkina as she bids to reach the Wimbledon last 16 for the first time.Jelena Ostapenko, who French Open nine years ago, routed Antonia Ruzic and will face world number one Aryna Sabalenka or McCartney Kessler, who meet later on Wednesday.