I'm going to do 8 matches that defined his season, I couldn't get it down to 5. In chronological order:
1. Australian Open Final: Djokovic def. Nadal 5-7 6-4 6-2 6-7 7-5
A 6-hour long epic battle, 2 days after playing a 5-hour semifinal against Andy Murray. Novak started the season defending his Australian Open crown. It was also the 7th straight win over Rafa in a final. Nole started the year very well. Things were looking good, the summer of disappointment was a long way away.
2. Roland Garros semifinal: Djokovic def. Federer 6-4 7-5 6-3
After the 2011 Roland Garros semifinal, when Roger broke Novak's winning streak, it was important to win the rematch, in straight sets even better. It was a very good performance by Nole. The body language showed how important this was for Nole. Not only because of what had happened the year before, also because Novak stated at the beginning of the season that his 2 goals were Roland Garros and Olympic Gold.
3. Roland Garros final: Nadal def. Djokovic 6-4 6-3 2-6 7-5
A final played over 2 days, interrupted by rain. This was a painful loss for Novak. He started slowly, and when he was on a roll, really dominating play, the match was suspended. The next day Novak, as usual, started slowly and lost the break advantage he had from the previous day. Rafa cruised and won his 7th Roland Garros title. Novak had failed to achieve one of his main goals for 2012.
4. Wimbledon semifinal: Federer def. Djokovic 6-3 3-6 6-4 6-3
This match was important on several levels: Novak failed to defend a grand slam itle, he lost the #1 ranking to Roger, once Roger won the title. For me it was distressing because I felt that Nole sort of gave up at some point. Roger was playing great, that's true, but Novak seemed without energy, out of sorts.
5. Olympics Bronze Medal match: Del Potro def. Djokovic 7-5 6-4
Another very painful loss for Nole: he failed to achieve his second goal for 2012, to win a medal for Serbia. Del Potro was painting the lines and playing fantastic tennis. Novak was outplayed.
6. USO final: Murray def. Djokovic 7-6 7-5 2-6 3-6 6-2
Yet another defeat in a grand slam final. Again the bad weather disrupted play. And bad scheduling meant that Novak had to play 3 days in a row, worse than Super-Saturday. He started the tournament really well, winning all his matches easily, saving energy, but it proved irrelevant. Again he started slowly and had to attempt a comeback, but his legs gave up in the 5th set and Murray was not to be denied this time.
7. Shanghai Masters final: Djokovic def. Murray 5-7 7-6 6-3
This match was very important, especially after all the disappointments during the summer. Again Novak started slowly and had to come back. He saved 5 MPs to win this title. One of the best matches of the year, in my opinion.
8. WTF final: Djokovic def. Federer 7-6 7-5
This match, and indeed the whole tournament were incredibly important for Novak. He had already secured the year-end #1, but some pundits commented that maybe the year-end #1 didn't really mean much, that maybe another player could reasonably be considered the Player of the Year. This narrative got momentum, and at some point the accepted narrative was that the WTF would decide who the Player of the Year was. So this tournament was crucial for Novak. He got to the final undefeated. The match was electrifying in its intensity: Roger won the first 9 points in about 2 minutes and he was up 3-0 in about 5 minutes...But again Nole turned it around and managed to win the title in straight sets.
Along the way, he beat Murray and Delpo, and accrued a lead of 2665 points over Roger and 4920 points over Murray. Not to mention proving to doubters that he was, not only the year-end #1, but also the Player of the Year.
After the USO final I thought Novak was going to have a confidence crisis, but quite the opposite happened: he won 3 titles (Beijing, Shanghai and WTF) and 3000 points after the USO final, much like Roger did in 2011. He also beat his main competitors, the ones who inflicted the most painful losses over the summer: Delpo, Andy and Roger. Unfortunately he didn't get the chance to play another match against Rafa... I'm hoping he'll get the chance in Australia... I'm also hoping that he'll use the momentum gained at the end of the 2012 season to solidify his position at the top of the rankings...Finally, I'm also hoping he won't start his matches so slowly this year, my heart is not getting any younger.