The comprehensive 7-6 (9/7), 6-4 defeat put paid to chatter of a quarter-final between the Argentine who won last year's US Open and top seed Rafael Nadal -- who plays his opening match on Thursday.
Del Potro, the former world number four, showed the effects of nearly eight months out of action after surgery on a wrist injury as he went down to the diminutive Belgian battler.
Rochus won despite 16 del Potro aces to earn a place in the second round.
Del Potro, 22, was playing for the first time since a fourth-round exit at the Australian Open in January. He underwent surgery in the US on May 4 and has made a slow recovery.
Rochus found a way back from 0-2 down in the second set after scraping through the first.
Del Potro is due to play next week in Tokyo as his comeback continues.
In other ties, Belgian qualifier Ruben Bemelmans set up a second-round contest against Rafael Nadal after beating fellow qualifier Frederik Nielsen of 6-2, 6-3.
Nadal, the world number one, who is making a debut appearance on court in the Thai capital after missing the two previous events through injury, spent a busy day Tuesday while his opposition was slotting into place.
The top seed, refreshed after six days at the beach resort of Hua Hin, planted a ceremonial tree as part of a project to seed a millions trees in honour of the Thailand's revered king.
The US Open champion then returned by air to the Impact Arena -- where the tournament is being held -- to begin adapting to the indoor surface.
Three other players booked places in the second round, with German veteran Rainer Schuettler easing by Brazilian Ricardo Mello 6-4, 6-2.
Israeli Dudi Sela defeated Konstantin Kravchuk of Russia 6-3, 6-4 while Kazak Mikhail Kukushkin had to go three sets to get past American Ryler DeHeart 6-3, 6-7 (4/7), 6-4.
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