Prior to the match, I wasn't inclined to give much of a chance to Serbia's No. 2 in the first Serbian quarterfinal on the men's side in Grand Slam history.
After all, there is a certain hierarchy in tennis, which, in short, entails that lesser players fold to the national No. 1. This phenomenon is clearly visible whenever Rafael Nadal plays a fellow Spaniard and whenever Roger Federer plays fellow Swiss Stanislav Wawrinka.
So far, the same pattern has emerged between Novak Djokovic and Janko Tipsarevic. However, they've only met two times prior to this US Open quarter, so we can hardly speak of a statistical pattern.
Another, perhaps more logical, reason to back Djokovic before the match is to take a look at his year and the way he's been playing and what has earned him a place as the overwhelming favourite at this US Open. By this account, Djokovic is the favourite against any player—and most certainly against a fellow Serb who isn't even in the Top 10.
However, watching the first two sets of the match, two things are immediately clear.
1) This isn't the Djokovic who's been nearly impossible to beat this year. His strokes are tentative, his trademark backhand is missing and his cross-court forehand is lacking.
2) Tipsarevic has a real shot at winning this. If anything, he should be leading the match 2-0 in sets. He was ahead most of the first set and dominating it, before he blew it in the tiebreaker.
The conclusion: Tipsarevic will win it?
As I've been writing, Djokovic has transformed himself. The cross-court forehand is back. He's no longer being dominated in the rallies, but dominating Tipsarevic. He's up 5-0 in about 25 minutes of play and Tipsarevic is being treated for a cramp in his thigh.
But for two-and-a-half hours, the world No. 1 looked more than beatable. Even if he steals this match in two snappy sets now, Roger Federer and Jo-Wilfried Tsonga's hopes of getting past Djokovic in an ensuing semifinal must have increased by a margin.
And who knows how long the superman version of Djokovic will stay on court? If he disappears and Tipsarevic's cramp is nothing serious, he will be ready to charge back and make it a five-setter.
The lesson for now? Despite Djokovic's wonder season, tennis stays an unpredictable sport with no absolutely guaranteed winners.