Captain Thomas Allen set up the second with a typically aggressive charge that was finished off by Sam Waddell for a handy 20-7 lead at the break.
Ten minutes into the second half, play was rightly held up for 15 minutes as a precaution by referee Amon Ripene after Bethlehem centre Tristan Downs-Hetet suffered a blow to his neck and was assessed on the field by doctors.
Bethlehem dominated after the restart, with second-five Nicolas Adams showing plenty of strength to score.
From the kick-off, barnstorming No8 Diardu Terblanche threw an excellent pass to Dylan Downs-Hetet on his own 10 metre line, and the winger cut through the Thames defence all the way to the goal line for a memorable try.
Terblanche then crashed over after picking up the ball from a scrum win, before a messy fracas reduced the visitors to 14 and they simply gave up.
Bethlehem are off to a fine start to the season but face their biggest challenge yet when they travel to Pukekohe High School on Saturday.
Meanwhile, Tauranga Boys' College got off to a winning start in the Chiefs Cup, beating St Peter's College in Cambridge 26-8, and this Saturday host St Paul's Collegiate.
Otumoetai College First XV defeated Tauranga Boys' College Second XV by 10-5 in the opening round of the 2014 Bay of Plenty division one competition, with first-five Jack May scoring all the points.
Bethlehem College 53 (Nicholas Bartlett, Sam Waddell, Nicolas Adams, Dylan Downs-Hetet, Diardu Terblanche, Jarrad Hawes, Sam Leppard tries; Leppard 6 cons, 2 pens) Thames High School 7