People stand in line to enter the US Open tennis tournament during a rainy day at the Billie Jean King National Tennis Center (ANGELA WEISS)Rain delayed the start play on the outside courts on Wednesday at the US Open, where top-seeded Alexander Zverev and women's fourth seed Coco Gauff headlined first-round action.The weather won't be a factor for Zverev and Gauff, who are scheduled to play the night session on the covered Arthur Ashe Stadium.Germany's Zverev, who followed up his maiden Grand Slam title with a runner-up finish to Jannik Sinner at Wimbledon, will take on 89th-ranked Italian Lorenzo Sonego while two-time Grand Slam champion Gauff faces Turkey's Zeynep Sonmez.Play started on Ashe with former Australian Open champion Madison Keys taking on Alina Korneeva.Under the roof on Louis Armstrong fifth-seeded French Open men's finalist Flavio Cobolli took on Argentine Francisco Comesana and women's fifth seed Mirra Andreeva -- the Roland Garros champion -- faced Indonesia's Janice Tjen.But reigning Australian Open champion Elena Rybakina's opener against 17-year-old wild card Thea Frodin, scheduled on the roof-less Grandstand court, was among the delayed matches.World number two Rybakina is chasing Aryna Sabalenka's number one ranking as well as a third Grand Slam title, having won her second in Australia in January.She reached the final of the WTA 1000 in Toronto this month before retiring from her quarter-final in Cincinnati with a painful heel injury that left her unable to walk without pain for several days.Frodin, ranked 585th, is making her Grand Slam debut. Although her competitive career is just beginning, her tennis talents were seen in "King Richard" the Oscar-winning film depicting Richard Williams and the rise of his daughters Serena and Venus Williams.A 12-year-old Frodin was the stunt and body double for Demi Singleton, the actress who played young Serena.bb/bsp