Fifteen-year-old American Coco Gauff pulled off a big upset at the Australian Open by eliminating defending champion Naomi Osaka in straight sets in the third round. This is only the third Grand Slam tournament of Gauff's career but already her second time reaching the fourth round. Osaka is a former No. 1 and a two-time major champion. Gauff already beat another former No. 1 in the first round this week when she got past Venus Williams. This followed another surprise result earlier in the day when Serena Williams was knocked out of the tournament.