Karlovic, at 2.08 metres the tallest man in tennis, was untroubled by Rochus, who stands just 1.67.
The resourceful little Belgian had won their past two meetings. But those 2005 dates were played before Karlovic began to find his form, culminating with three titles earned last season.
It took just 64 minutes for the Croatian to go through for only his fourth victory of a slow-starting season.
2004 finalist Juan Carlos Ferrero fell victim to a bout of food poisoning as the Spaniard limped out 7-5, 6-1 to Teimuraz Gabashvili.
Ferrero, who lost the final four years ago at the Ahoy stadium to Lleyton Hewitt, was unable to mount an attack in a listless performance due to his condition.
"I hope this match is just a one-off, it's the first bad one that I've played all year," said the 28-year-old ranked 20th.
Ferrero has been lifting his game this season after once standing atop the rankings.
The veteran played the January final in Auckland, losing to German Philip Kohlschreiber and got to the fourth round of the Australian Open.
"I played some good points, but I also made a lot of mistakes," he said of his effort against Gabashvili.
Fellow Spaniard Rafael Nadal is making his Dutch debut as top seed, with with Iberians David Ferrer, Fernando Verdasco. Tommy Robredo and Feliciano Lopez all still in the mix.
The Ferrero match ended after 74 minutes, with Gabashvili going through. The Russian had a patchy effort last season, playing a first-ever quarter-final but also losing 21 times in the first round.
Michael Berrer defeated fellow German Matthias Bachinger 6-3, 6-2.
By Bill Scott, dpa