Iga Swiatek, hot favorite for the women's title, and men's dark horse Jannik Sinner swept into the third round of the Australian Open before nine first-round matches were started as the weather continued to wreak havoc at Melbourne Park on Wednesday. World number one Swiatek overcame Camila Osorio 6-2 6-3 under the roof on Rod Laver Arena and Italian Sinner waltzed past Tomas Etcheverry 6-3 6-2 6-2 on the similarly protected John Cain Arena. Rain kept the players off the outer courts for four hours after the scheduled start, however, adding to fixture congestion triggered by extreme heat and storms on Tuesday when nine matches did not get started and two could not be completed. Swiatek headlined the action that was possible early on Wednesday and was the first to admit that the scoreline did not reflect the difficulty of her contest against the 21-year-old Colombian. The Polish top seed set off at a canter and was 4-0 up before Osorio found her range with her groundstrokes and scooted around the court to put huge pressure on Swiatek's serve. Two breaks of serve got the Colombian on the scoreboard at 5-2 but Swiatek broke back to win the opening set and fended off another break point in the opening game of the second. "It was really intense physically and Camila was running to every ball, she didn't give up," said Swiatek. "She didn't give me many points for free, so I needed to really work for each one of them, but I'm happy that I was consistent in being proactive and trying to just play a little faster to put pressure (on her)." Swiatek always had the measure of Osorio's serve, however, and even when she was broken serving for the match for the first time, a third round meeting with former US Open champion Bianca Andreescu or Cristina Bucsa never looked in doubt. Greek sixth seed Maria Sakkari had a much bigger scare on Margaret Court Arena against 18-year-old Diana Shnaider and was forced to come from a set down to beat the Russian teenager 3-6 7-5 6-3 over more than two 1/2 hours. "It was a very high level from both of us, she played an amazing match, she's very talented, very promising," said Sakkari, before joking that Shnaider should consider giving up her college eligibility in the United States and turn professional. Sinner, who has reached the quarter-finals of all four Grand Slams but never gone any further, could hardly have shown better form as he briskly dismissed Argentine Etcheverry. Strong and aggressive, the 21-year-old fired 32 winners and converted all five of his break points to set up a third-round meeting with Lloyd Harris or Marton Fucsovics in an hour and 44 minutes. "For sure, the level today was good, I served well, I returned good as well as I think he is a very good server so I'm very happy to be in the next round," Sinner said. "I'm very happy to play on this court with the roof, hopefully it won't rain in the next days."