Last week he won the ATP World Tour Finals with partner Daniel Nestor for the second time, bringing down the curtain on a partnership with the Canadian which also earned them two Wimbledons and one French Open title.
This week, however, all his personal achievements will be put to one side when he plays for Serbia in the Balkan country's first Davis Cup final, against France in Belgrade.
"It's a completely different achievement," said Zimonjic, who has won 23 of his 30 doubles rubbers since making his debut in the competition for the former Yugoslavia against Benin in 1996.
"But it's the biggest achievement that Serbia has as a country in tennis. I'm looking forward to... playing the biggest final in our tennis history.
"It would mean everything to the players, to the Federation, to people there, to say we are world champions. Maybe not all of them knew what is Davis Cup. Now I believe they know that it's like a world championships in tennis."
Zimonjic, who will most likely partner Janko Tipsarevic or Viktor Tricki in Saturday's doubles, plodded the lower levels of the men's Tour after turning pro in 1995, hardly rising above 200 in the rankings.
By the time he beat Agassi in 2004 he had already made the decision to concentrate on the doubles arts.
"It wasn't so much a choice," he said ruefully. "I didn't have sponsors. I didn't have chances to hire a coach that could travel with me. I never had a chance to concentrate on it for six, seven months.
"The money I was making in doubles was being re-invested in myself so that I could keep playing the singles circuit."
However, what was merely a means to an end suddenly offered Zimonjic the chance to shake off the journeyman tag and establish himself as one of the world's best doubles players.
With a variety of partners he began collecting doubles titles and in 2005 he became a Grand Slam champion when partnering Karerina Srebotnik to the Wimbledon mixed crown.
In 2008 he teamed up for the first time with Nestor, winning Wimbledon and finishing the year as the world's number one duo. Last year they won nine titles and seven more followed this year, including the French Open.
Like many players from Serbia, Zimonjic's route to fame and fortune was a tough one with crumbling sports facilities and the region being torn apart by war.
Training took place in a drained swimming pool in Belgrade - the same makeshift arena that provided an improvised court for former women's world number one Ana Ivanovic.
"That was actually a good place to practice," he recalled. "There were no indoor courts and the swimming pool was ideal. It was actually quite luxurious compared to what I'd been through.
"I was playing tennis in the worst time for the country. The worst time for athletes. We had embargo sanctions. We could not compete as juniors. I had to fly out of Budapest, which is six hours by mini-van.
"Every time I had to leave the country, six hours to Budapest, then fly somewhere. It was really rough and difficult to get visas to travel. Then there was the army and the passports, it was difficult to be a tennis professional."
Out of adversity, however, Serbia has become a tennis powerhouse with world number three Djokovic leading the team this week against France.
France may have a depth rivalled only by Spain and facilities to envy, but Zimonjic believes Serbian team spirit could hold the key.
"There is no comparison with us and France, they are nine times Davis Cup champions," he said.
"They have eight or nine players that can play any day in the Davis Cup. But we are strong. We are good friends, all four of us, off the court, which helps a lot in situations like this coming up."