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.
Gael Monfils , the 13th seed, brushed aside Alex Bogomolov Jr . 6-4 6-1 in their first-round match at the Rome Masters, with Fernando Verdasco also winning through.
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 Juan Carlos Ferrero in the second round after the Spaniard beat South Africa’s Kevin Anderson 6-4 7-5.
Verdasco was another to seal his progression through to the second round on Monday after Alexandr Dolgopolov retired after losing the opening set 6-0.
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 David Ferrer , who received a bye through to the second round.
Australia’s Bernard Tomic was also victorious on Monday as he roared back from a set down to beat Santiago Giraldo 4-6 6-2 6-4.
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 Novak Djokovic , who received a bye through to the second round.
12th seed Nicolas Almagro proved too strong for big-serving Marin Cilic as he completed a 6-2 3-6 6-0 win over the Croatian player. Almagro has reached two finals on clay this season, including a victory in Sao Paulo.