Golden State Warriors forward Draymond Green knows exactly what it feels like to win and to lose.

Green attended the US Open to watch Serena Williams' quarter and semi-final games on Wednesday and Thursday.

He was able to see her win the first game, then lose the second to Karolina Pliskova in the semi-finals. He wasn't happy about it because he was cheering Serena on, and told TMZ Sports how he felt after the loss.

I'm mad Serena lost. I hate to see Serena lose, man.

Green knows Serena has been dealing with a knee injury, and understands how stories in sports don't always have happy endings.

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Ain't your day every day. … Can't win 'em all. She's still the greatest.

He understands as much as anyone that you aren't defined by one loss in pro sports. He did after-all help the Warriors complete a historic 73-win season only to lose in Game 7 of the NBA Finals.

Green knows Serena will be back, because that's what great athletes do.

The Warriors will be back also after their loss last season.