Having been promoted at the end of last term, the priority for head coach Marcus Di Rollo was to beef up the Watsonians pack for the rigours of the top flight.
He brought in the likes of Sean Crombie, Ewan McQuillin, Craig Borthwick, Diarmuid Dee and Euan Dods and at the weekend they showed why.
The home pack took the game to the reigning champions and their performance in the set piece set up the win in front of a healthy crowd.
No 8 Rory Drummond also carried the ball well and got his team on the front foot. Behind the scrum former Edinburgh Rugby man King and Club XV cap Scott McLeod gave defensive stability in the centre.
King said: “I was really pleased with the way the guys played.
“There is still plenty to work on and this is just one game, but after promotion you cannot really ask for much more than beating the champions.
“I thought the pack were outstanding and the experienced guys like Sean and Craig led from the front and put in a good shift.
“In this league you need to have a hard edge to survive and we showed that in patches in this win.”
Heriot’s never gave up and in centres Josh Laird and Liam Steele they had two of the best players on show, the former showing what he can do after injury problems.
Callum Marshall, on his league debut having joined from Selkirk, also showed up well while they managed to grab a losing bonus point late on.
In a first half that never really got going, Scott kicked two penalties for the hosts and stand-off Alex Hagart responded for Heriot’s.
Drummond was in the sin bin for a spell while Heriot’s back-row Dylan Mason was yellow carded for a high tackle just before the break.
While he was off the field Watsonians went 13-6 up in the 43rd minute thanks to a converted try by Irishman Dee. By this point the home pack was on top and they were awarded a penalty try 15 minutes later.
That made it 20-6 before a Steele converted try got Heriot’s within seven points.