Caroline Wozniacki is a really good sport.

The No. 5-ranked women's tennis player has carved out a pretty good niche for herself, not only with her on-court play but with her social life - once having been No. 1 golf player Rory McIlroy's fiancée and now is reportedly dating the best defensive player in the NFL in JJ Watt.

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But Saturday night, she found herself playing the role of second banana as world's No. 1-ranked Serena Williams accompanied her to a Taylor Swift concert at a festival in Hyde Park in London, Fox Sports reported.

When Swift was singing her hit single, "Style," Williams was invited on stage with other celebrities Kendall Jenner, Karlie Kloss, Gigi Hadid, Martha Hunt and Cara Delevingne, Entertainment Weekly reported.

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Actress Emma Watson joined Swift backstage, EW added.

As for Wozniacki? She apparently did not get an invite, as USA TODAY Sports' For the Win noted, and settled for a Twitter pic with Kloss and Williams.

The tennis stars embark on, perhaps, tennis' biggest stage when Wimbledon begins today. Serena Williams plays No. 113 Margarita Gasparyan as she looks for her third Grand Slam victory of the year and 21st major of her career, For the Win reported.

Wozniacki begins play on Tuesday when she takes on No. 65 Saisai Zheng. It's an interesting twist on preparation before a major. Players of yesteryear might scoff at Serena's public display, saying that playing Wimbledon should be treated as a business trip.

But obviously, Williams will be under enough duress as she looks to continue her quest for the calendar Grand Slam and the figurative title of greatest female tennis player ever.

And Wozniacki again looms as a spectator in Serena's theater.