A fan cried out some advice that Serena Williams says helped her win a very tough fourth-round match.

The No. 1-ranked Williams was down a set and trying to find a solution — when she heard a voice.

"Someone in the crowd was like, 'Come on Serena use spin!' and I was like, 'OK,'" Williams said after coming back 2-6, 6-3, 6-2 to beat Garbine Muguruza and reach the Australian Open quarterfinals.

"There's coaches everywhere out here! Thank you guys, you really helped me," Williams said during her on-court interview after the match.

The 18-time Grand Slam winner scanned the stands of Rod Laver Arena where she recalled hearing the voice and then pointed to someone in the crowd: "It was you? Thank you. Thank you!"

The interviewer, retired Australian player Rennae Stubbs, then suggested she give the fan a cut of the prize money.

"Five percent?" asked Stubbs.

Williams laughed off the suggestion. "Come on Renee!"

By Jocelyn Gecker -- http://twitter.com/jgecker