Even the most intense burning competition can't threaten their sisterly bond.

Their sweaty, sisterly bond.
Their sweaty, sisterly bond.

In case you haven't been following the U.S. Open this year, here's a refresher: it's tennis. Also, Serena Williams is killing it. She's poised to become the fifth player in history to win the coveted Grand Slam.

In the process, she defeated her sister Venus in the quarterfinals on Tuesday night. The two embraced warmly after the match, proving that there weren't any hard feelings. It's not surprising, considering they've been competing alongside and against each other their whole lives. To hammer that point home, Serena took to Instagram to post this adorable collage the next day.

Sources: Serena Williams