Melbourne, Jan 18 : World No. 1 Novak Djokovic overcame a ferocious challenge from Alexei Popyrin on Wednesday, while defending women's champion Aryna Sabalenka eased through to the Australian Open's third round. Djokovic, the 10-time tournament champion, has not produced his vintage form at Melbourne Park and for the second straight match was pushed to four sets. But he defied body aches and heckling in the crowd to defeat the gallant Australian 6-3, 4-6, 7-6 (4), 6-3 in three hours and 11 minutes. The 43rd-ranked Popyrin rued being unable to convert four set points in the 10th game of the third set before Djokovic clinched the match and let out a triumphant roar. "I don't think I played at the highest level, but credit to him for coming up with the right strategy," Djokovic said. "I haven't been playing my best, still trying to find form." Fourth seed Jannik Sinner continued his bid for a first Grand Slam title with a second consecutive straight sets victory after downing Dutch qualifier Jesper de Jong 6-2, 6-2, 6-2 in one hour 43 minutes. The 22-year-old Italian dominated in all facets and lost just 10 points on serve, while breaking six times. "It doesn't really matter who you play against. You fear nobody but have a lot of respect for everyone," Sinner said. "This is what I try to show to everyone." Australia's main hope Alex de Minaur continued to impress after beating Italian Matteo Arnaldi 6-3, 6-0, 6-3 in a one-sided romp. The No. 10 de Minaur won 11 straight games during one dominant stretch to improve his record this season to 5-1, including a victory over Djokovic at the mixed teams United Cup. No. 5 Andrey Rublev and No. 7 Stefanos Tsitsipas also made it through to the third round as they continued their quest for a maiden Grand Slam title. In the women's action, Sabalenka powered past 16-year-old qualifier Brenda Fruhvirtova 6-3, 6-2 in 67 minutes. It was the Belarusian's ninth straight victory at Melbourne Park as she bids to become the first woman to successfully defend her Australian Open title since Victoria Azarenka in 2013. "I'm not thinking about confidence. I'm just trying to play my best," said second seed Sabalenka. "I just try to focus on myself and fight for every point." Fourth seed Coco Gauff beat fellow American Caroline Dolehide 7-6 (6), 6-2 to underline her title credentials. The U.S. Open champion was made to work in a tense first set and looked on the brink when Dolehide had the chance to serve it out at 6-5. But Gauff broke then raised her level in a gripping tiebreak to dent Dolehide's resistance. "It was really hard," Gauff said. "If you give her something short, she's going to punish you for it, so if I could go back and do something I'd change that." The 19-year-old Gauff will next play compatriot Alycia Parks, who upset 32nd-ranked Leylah Fernandez in straight sets. But sixth seed Ons Jabeur crashed out after being thrashed 6-0, 6-2 by Russian 16-year-old Mirra Andreeva in just 54 minutes. Jabeur, a three-time Grand Slam finalist, had no answer for a red-hot Andreeva, who continued an eye-catching debut at Melbourne Park with her first victory over a top-10 player. Former tournament champion Caroline Wozniacki and 16th seed Caroline Garcia, who beat Naomi Osaka in the first round, were eliminated. On Thursday, No. 1 Iga Swiatek and men's second seed Carlos Alcaraz will be in second-round action, while China's top-ranked player Zheng Qinwen faces Katie Boulter. /IANS