Strangely, going down to 14 seemed to inspire Scottish and guided by the boot of Dan Newton and an interception try from wing Peter Homan, they actually moved into a 13-10 lead.
Tom Pascoe and Thomas Young replied with further home scores with Humberstone doing the rest. Dai Flanagan added a late penalty to secure the win but in the final few minutes, Mike Doneghan went over for Scottish with replacement Lee Millar converting.
It meant the visitors earned a losing bonus point and while Pontypridd pounded the opposition line late on with Scottish down to 13 after full back Ollie Lindsey-Hague was sin binned, they were unable to claim what would have been a crucial fourth try.
After former Scarlets fly half Newton had missed an early penalty chance for the visitors, Pontypridd moved into a 10-0 lead. Humberstone was successful with his first penalty effort before putting a delightful kick through for Jenkins to cross for the first try of the day.
From a Pontypridd line-out on the Scottish 22, the visiting defence spread themselves towards the right hand touch line but when Humberstone received the ball, he spotted Jenkins in oceans of space on the left wing. His innovative chip ahead was collected and when the fly half nailed the touchline conversion, it completed a satisfying first quarter for the home side.
Humberstone then missed a chance to extend the lead with a second penalty but just before the half hour, the complexion of the game changed completely. A ruck just inside the Scottish half saw Pontypridd second row Craig Locke upended. Play was stopped with the end result seeing Best red carded by referee Sean Gallagher.
Luckily for Pontypridd, man of the match Locke was fit to continue but far from being hindered with 14 men, the red card actually saw Scottish enjoy their best period of the game.
Newton kicked penalties either side of the interval and when Pontypridd gifted the visitors a try, Scottish were ahead. It was Christmas come early for the men in red, Pontypridd wing Chris Clayton throwing a loose pass and Homan racing clear to dot down under the posts. Newton converted but his side weren't ahead for long.
Pascoe, a first half replacement for Gary Williams, darted over after good approach work from Humberstone before a huge forward surge saw Young emerge with the ball over the try line. Captain for the day Humberstone added both sets of extras and at 24-13 with an hour played, the score line looked a lot more comfortable from the home side's perspective.
With a growing injury list going into this game, Pontypridd's resources were already stretched. And they were further hindered in the second half when try scorer Pascoe was forced off. Dai Flanagan was his replacement with Humberstone moving to centre.
It was hardly ideal circumstances for the home side but with Scottish now struggling to get back into the game, Flanagan's late penalty pushed Pontypridd further clear.
The only downside was Doneghan's late effort which gave Scottish something to take into next weekend's return fixture.
Pontypridd: Tries: Jenkins, Pascoe, Young; Convs: Humberstone (3); Pens: Humberstone, Flanagan.
London Scottish: Tries: Homan, Doneghan; Conv: Newton, Millar; Pens: Newton (2)