Sam Sherriff (22) and a relatively quickfire 19 from 13 balls by Connor O'Leary were the only other scores of note, as Collegiate seemed 40 runs short of putting the competition leaders under pressure.
However, the aggressive Dinwiddie, who can illicit troublesome bouncers out of that pitch, struck a big blow when he bowled the key man Lance in the third over.
United recovered with Allistar Bostock (35 from 120 balls) willing to take the risk of advancing down the track to speed up the glacial scoring pace, following on from D Hussey (20 from 30) guiding them to 45-1 in the 17th over and seemingly on track.
However, Collegiate's bowlers hit back to leave United reeling at 46-4 with representative players Greg Smith and Chris Sharrock back in the shed.
James Pennefather is not considered to have the same aggression as Dinwiddie, but Saturday he was on-point and collecting the scalps with an outstanding effort of 4-25.
It was the experienced Brendon Walker who again settled United with 45 from 61 balls, however upon reaching the 40's, the game took another twist as bad cramp saw Walker limp off, with Lance keen to get him back out there quickly if the momentum swung the other way.
Fears were justified as after a stretching routine and a drink of salt water, Walker was heading back out when his fellow regulars Gerard Hobbs and Robbie Power fell to Sherriff and the on-fire Pennefather in rapid order, leaving United 131-8 in the 43rd over with the final ten runs off 24 balls seeming like a mountain to climb.
Dinwiddie came back and with a perfect yorker bowled Walker, with last man Dylan Martin striding out.
Martin would have a go initially, managing a couple of singles and a two over the top off the fizzing Dinwiddie and Connor O'Leary, but after playing and missing and nearly being caught out, the cries came from the shed to block the final delivery rather than risk all for the win.
Collegiate never gave up, and despite a couple of fielding mishaps behind the stumps, had pinned their more fancied opposition down, with good line and length complimented by enthusiasm in the field.
"There's a lesson in it," said coach Warren Marr, who went on as a replacement fielder for the finale.
"My motto is, 'always add two wickets to the score'. If you can get one, then you put the pressure on, and we did.
"I'm very proud of them."
United did have a bit of bad luck as during Walker's innings the ball struck a helmet, which under the rules should constitute five runs, however, it was not picked up and singled by the umpires.
However, Lance was not looking to make excuses about that moment or the difficulty of Collegiate's wicket in the first half of the summer.
"It's always decent, there's never too much in it.
"It was a hard game, [Collegiate] played well, came back well.
"We can't do anything now, it depends on what happens elsewhere."
Both Collegiate and Marist will need big wins with healthy bonus points in their last games when the league resumes after Active Physio Wanganui's representative game this coming weekend, with United having the final bye.
However, Marist must face a St Johns Tech team who finally hit their stride after a poor run of form, posting the biggest score of the league so far with their 243-6 leading to a big 144 run win over an undermanned Matt Burke Engineering Marton Saracens Premiers at Victoria Park.
Batting time, Tech always seem to do their best when a good launching pad enables them to overcome the inevitable mini-collapse, so there are runs left to be scored at the end.
So it proved with Calum Coker (60) anchoring the top of the order, supported by Akash Gill (20), and although captain Dominic Lock and the Watkin's - Kane and Jessica - were out of sorts, along with the promoted Ross Kinnerley departing quickly, master blaster Nick Harding was freed up to play his natural game.
Harding smacked 99 not out, supported by Matthew Bennett (25no), but missed his century in bemusing circumstances when he smashed a six to lose the ball in the final over, and then after a break, the last delivery could be considered "wide-ish" but was not called.
Harding had ridden his luck with three dropped catches in his innings, while Marton's bowlers Daniel Ford (2-59) and Phil Galpin (2-63) were looking their team's best until copping that stick.
In response, Marton were hanging tough at 59-1 after 19 overs and then 71-1 after 23 with Jason Harris (26) and the in-form Josh Trillo (37) keeping up with the target.
However, both fell to catches off the tricky Jessica Watkin (4-30) and from there the remaining players tumbled quickly to be out of there in 37 overs, with no other batsman dragging their score above five.
Harding (2-3) joined Watkin in cleanup duty.
While an understrength Marton were always going to struggle with the bat, Lock was most pleased his team had done the business with the willow after a run of poor scores.
"Finally. We built the innings well.
"Our openers batted 17 overs, then with Nick coming out late.
"[Marton] used all their bowlers early, to be fair."
Tech would like to make it two wins in a row in the league, in turn denying Marist their small mathematical chance on claiming the title off United.
"We don't want Marist to win. Not one little bit," said Lock.
"We've still got something to play for. To build up for the more important games coming up."
Results
Collegiate 140-8 (A Dinwiddie 40, H Cave 25, S Sheriff 22, T Lance 3-44) drew with United 137-9 (B Walker 45, A Bostock 35, D Hussey 20, J Pennefather 4-25, C Greatbatch 2-8, A Dinwiddie 2-21).
St Johns Tech 243-6 (N Harding 99no, C Coker 60, M Bennett 25, A Gill 20, D Ford 2-59, P Galpin 2-63) beat Marton 99 (J Trillo 27, J Harris 26, J Watkin 4-30, N Harding 2-3) by 144 runs.