Serbian Novak Djokovic has withstood a tough test from countryman Viktor Troicki, winning their US Open first-round battle in five sets.
The third seed got off to an ideal start, winning the first set before the 47th-ranked Troicki won the next two, meaning Djokovic could only win if the match went the full distance.
But the steely Djokovic prevailed and served out the match to win 6-3 3-6 2-6 7-5 6-3.
The world No.3 seemed to be struggling with the high temperatures at Flushing Meadows, applying bags of ice to his forehand at the change of ends.
But his game began to heat up when he needed it most in the final two sets.
Troicki backed himself to beat his Davis Cup team-mate, hitting 66 winners including 23 aces, but his riskier stroke play also accounted for 61 unforced errors.
Djokovic was far more conservative in his baseline rallying, hitting 41 winners and 43 unforced errors, and interestingly won just one more point in total than Troicki for the match.
Both players converted five from 14 break point chances; one of Troicki's breaks came in the first game of the final set before Djokovic broke him back twice in succession to claim the ascendancy.
Marcos Baghdatis was the first major casualty in the men's tournament after he lost to Frenchman Arnaud Clement 3-6 6-2 6-1 4-6 5-7 on Tuesday.
The No.16 seed led 3-1 in the fifth set but could not hold off his unseeded opponent, who closed strongly in steamy conditions at Flushing Meadows.
Clement moves to the second round, but will find it extremely difficult to back up the win after working himself to near-exhaustion in the marathon 207-minute match.
The Frenchman set the early pace to cruise through the first set but Baghdatis hit back, snaring the next two sets for the loss of only three games.
Clement broke when it mattered to take the fourth set and send the match to a deciding fifth set, which Baghdatis broke open early to lead 3-1.
But the plucky Clement would not be denied, breaking back and holding serve to level the set 3-3.
Baghdatis dug deep to hold serve at 4-5 down, but was undone two games later with a wide forehand on the third match point as the heat and Clement's nagging persistency finally undid the Cypriot.
There were no such problems for 10th seed David Ferrer as he cruised past Ukraine's Alexandr Dolgopolov 6-2 6-2 6-3.
American 19th seed Mardy Fish endured a rollercoaster match against Czech Jan Hajek, but won 12 of the final 13 games to win 6-0 3-6 4-6 6-0 6-1.
Feliciano Lopez, the 23rd seed, was a straight-sets winner over Colombia's Santiago Giraldo 6-4 6-4 6-4, but there was no such joy for 24th seed Ernests Gulbis and 30th seed Juan Monaco who lost to Jeremy Chardy and Peter Polansky respectively.
Czech 28th seed Radek Stepanek was another seed to bow out as he fell to Frenchman Julien Benneteau 6-4 6-2 4-6 6-4.
Other winners on day two of action include Eduardo Schwank, Tommy Robredo, Daniel Gimeno-Traver, Benjamin Becker, Benoit Paire, Philipp Petzschner, Adrian Mannarino and Pablo Ceuvas.