6ft 9in Isner began the fightback by winning the second set 7-3 on the tie-break. He threw down 10 aces against Munich title winner Kohlschreiber to set up a match in the second round against Italian Andreas Seppi at the Foro Italico.
Monfils produced four aces and a first-serve percentage of 80 as he outclassed his opponent, ranked at number 44 in the world.
The Frenchman took the opening set courtesy of two breaks of serve, and Bogomolov failed to get any real rhythm.
Monfils capitalised with two of his 10 break points in the first set, but was more clinical in the second set as he pounced ruthlessly on every mistake from his opponent.
It was a regulation victory for the world number 14, who will next take on
Verdasco, who beat Rafael Nadal at the Madrid Masters last week, was utterly dominant against an off colour Dolgopolov, who was forced to retire after failing to win a single game.
The Spaniard was unwavering in his power and intensity from the back of the court, and will next take on compatriot
Tomic lost the opening set with a solitary break separating the players, but he responded superbly to take the second 6-2 with an unerring rhythm on serve and powerful returns.
Giraldo, the world number 51, could not raise his level again sufficiently in the deciding set as Tomic took it 6-4 to set up a match against world number one