Moment 5: Novak Djokovic hits the all-or-nothing forehand return heard 'round the world 

WATCH: Novak Djokovic sits at the Tennis Channel desk after his record-setting 23rd Grand Slam title.

Is the Big 3’s Grand Slam title race finally over? It appears so. Now that we (probably) know the winner, we’re looking back at the times when this two-decade marathon might have gone a different way.

For more on GOAT Race, a 10-part series leading up to Wimbledon, read...

• Moment 1: 2007 Wimbledon final: Nadal “seizes up” with break points in the fifth
• Moment 2: 2008 Wimbledon final: Federer’s four-hour comeback comes up one break point short
• Moment 3: 2010 US Open semifinal: Djokovic “closes his eyes” and hits two huge, match-saving forehands against Federer
• Moment 4: 2011 Roland Garros semifinal: Federer stops a 41-match win streak, and wags a finger

5. 2011 US Open semifinal: Novak’s return heard 'round the world

If you had to pick a defining shot of the 21st century, what would it be? Novak Djokovic’s go-for-broke crosscourt forehand return, hit when he was down double match point at the end of this US Open semifinal, has to be in the conversation. The defiant head nod beforehand; the “give me some love for a change” attempt to rally the pro-Federer crowd afterward; and, most of all, the ability to smack a blazing winner with everything on the line: It was Djokovic in a nutshell, even if he had no idea how he did it.

“That forehand return, I cannot explain because I don’t know how it happened,” he said. “I read his serve and I was on the ball and I had to hit it hard, and it got in, luckily for me.”

Federer, famously, emphasized Djokovic’s good fortune.

“To lose against someone like that, it’s very disappointing, because you feel like he was mentally out of it already,” Federer said. “Just gets the lucky shot at the end, and off you go.”

Federer’s bitterness was understandable. In a surreal repetition, he had just lost to Djokovic in a US Open semifinal after having two match points for the second straight year. A few months earlier, when the two met in the semifinals at Roland Garros, Federer came up with the perfectly placed serves he needed to keep Djokovic from getting a racquet on his return. This time he gave him two swings, and Djokovic took them.

Lucky or not, the Serb played the match points as well as they could be played in New York. While his cannonball forehand is the shot we remember, his return on the next point was almost as good. Federer hit a bullet first serve into his body, and Djokovic somehow got out of the way and reflexed a backhand down the middle with pace. And even if Federer was right that Djokovic was “mentally out of it already” by the time he was down match point, the Serb often went for broke on his returns when he was facing the Swiss. Djokovic’s return was his biggest weapon, and he used it for all it was worth.

While the two Open semifinals were bizarrely similar, the status of each player had changed over the previous 12 months.

In 2010, Djokovic had one major title to Federer’s 16, and he was just trying to get back into a Grand Slam final for the first time in more than two years. He would lose that final to Nadal the following day.

In 2011, Djokovic was the No. 1 seed at the Open for the first time, and was capping a nearly perfect season. This time, after beating Federer, he would turn around and beat Nadal the next day to put a final stamp on his rise to the top. He had four major titles now, which left him 12 behind Federer and six behind Nadal. Whether Djokovic knew it yet or not, the chase was on.