"Good time to pull it out," Lock said.
"It was just eyeing up the short boundary and it was coming off alright."
Tech's run rate stayed above six an over but thoughts of 300 were unrealistic as Lock kept running through partners, Weraroa eventually targeting everyone else to strand him.
Leg spinner David O'Brien would claim five wickets, getting through the defences of Jessica Watkin and Ross Kinnerley, while having catches picked up out of Tech's lower order.
That same lower order had only managed 18 runs for five wickets from their previous game, but Lock kept hitting for as long as he could, with the best support coming from Caleb Greene (20), the returning Calum Croker (20) and Kinnerley (18).
"I was getting a bit worried but everyone got starts. They bowled in the places we could hit the ball," Lock said.
When he went to a caught-behind off O'Brien in the 37th over, Tech's 236-8 was impressive for the run rate but a concern if they folded with plenty of unused overs, given Weraroa proved two weeks ago against Property Brokers United that they can run down decent totals.
Devon Purvis made a solid cameo with 18 runs from 19 balls, including two sixers, but was the last man to fall with six overs still available.
Needing to put the presssure on, Tech's bowling started strongly once again with the Kinnerley and Harding duo - the latter getting dangerman Matthew Good out cheaply - while Kinnerley snatched a caught and bowled to remove Carl Trask (20).
The pair cleaned out the rest of the top order to have Weraroa teetering at 60-5 when Lock took them both off with two overs each left up the sleeve, yet he soon had a dilemma.
Wade Anderson, as he did against United, was being stoic at one end with 59 from 77 balls, and while Watkin was bowling measly spinners with 1-26 from her 10 overs, Tech had lost the pace of Greene and Tim Czerwonka was expensive with his only six deliveries, as the game stood poised at 161-7.
"Chicken [Greene] was injured in the first over he bowled, so I had to finally take the gloves off, bowl with the seam up, first time in two years," said Lock.
The skipper's reluctance to continue with his own bowling development due to injuries has been often discussed amongst the various Whanganui club teams, but with no preparation he came up trumps in a three-over spell.
Anderson was trapped in front, captain Huka Kahu could not repeat his heroics from the United game and was bowled, and then Krunal Modi also lost his stumps for the favourites to be out of there in 37 overs.
Tech's victory marked a weekend of upsets where three teams were beaten by the side who finished below them on the points table.
In the other semifinal, Levin Old Boys defeated Paraparaumu CC by two wickets, bowling them out for 166 on the back of a 5-33 performance by seamer Nick O'Brien, and then soldiering through to 169-8 in the 40th over.
The key partnership was between Dion Sanson (42) and Ryan Taylor (40), while the match was saved for Levin by a blast from Liam Pinfold, making 29 not out from 16 balls at No10.
Given this competition has really shown that matches are decided by 2-3 individuals standing up when it counts, Lock rated Tech's chances of back-to-back wins on the road come finals day on February 6.
"I don't see why not. We've beaten [Levin] already this year, and we just had an off day with Paraparaumu."
Semifinal results:
Tech 256 (D Lock 115, N Harding 24, C Greene 20, C Coker 20, D O'Brien 5-48) bt Weraroa 165 (W Anderson 59, C Trask 20, D Lock 3-3, R Kinnerley 3-36) by 91 runs.
Paraparaumu 166 (S Windle 35, C Emmott 33, N O'Brien 5-33) lost to Levin Old Boys 169-8 (D Sanson 42, R Taylor 40, L Pinfold 29no, R Knight-Densem 4-29, J Singh 3-35) by two wickets.