In a decade to remember, 2019 didn't disappoint as the closing act. Click here to review the Top 10 moments from the final season of the 2010s.
First it was boos, then it was cheers. Daniil Medvedev pretty much got it all at the US Open.
The Russian riled up the crowds during his third-round match against Feliciano Lopez, arguing with the umpire, gesturing at spectators and holding his ear to invite more disapproval from the stands.
And he wasn't done. Medvedev taunted the crowds further in his post-match interview. "I won because of you," he told them, drawing even more rancor.
Together with Stefanos Tsitsipas having a first-round meltdown and calling the umpire a ''weirdo," and Nick Kyrgios's usual antics, it prompted questions about the temperament of the game's newer generation.
But once off the court, Medvedev was contrite about his behavior. On court, building on his form coming into the event, he got to the final against Rafael Nadal and almost won, coming from two sets down to force a tight fifth set before falling 7-5, 6 - 3, 5-7, 6-4, 6-4 in a gripping, grinding encounter that gave Nadal his 19th Grand Slam and second of the season.
Yet the biggest turnaround might have come in Medvedev's post-match speech, where he thanked fans for helping him get back in the contest.
"Now I'm saying it in a good way -- that it's because of your energy that I'm in the final," he said, getting wild applause. "You see that I can also change, because I'm a human being."
He didn't win the event, but he won a lot of fans -- and that would have seemed far unlikelier when the second week began.