Serena Williams pays tribute to big sister Venus

Following Venus Williams' three-set loss in the first round of the U.S. Open on Monday, her younger sister Serena Williams paid her tribute on social media.

"Strength, courage, determination, class, perseverance, inspiration... there's not enough words to describe how proud I am of you @VenusWilliams," Serena Williams wrote on Instagram with multiple photos of her sister in action. "P.S. I hope to be like you."

Venus Williams has been making a comeback at age 45 after 16 months away and was granted a wild-card entry into the singles bracket of the U.S. Open. She won a match at the DC Open last month.

Serena Williams remains on the official retired players list.

Venus Williams has 819 wins on tour and 49 career titles, including six Wimbledon titles and two at the U.S. Open. Serena Williams has 858 career wins and 73 titles. Of her 23 major titles, seven have come at Wimbledon and six have been at the U.S. Open.