The tricky midfielder, once of Basford, gave his side the lead just before the half hour with a smart free kick before repeating his exploits only three minutes later, in front of watching manager Nigel Clough.
Nathan Caine then wrapped up the win for the young Stags shortly before half-time when he found himself on the end of Jimmy Knowles’ low cross.
Despite the defeat, United boss Steve Chettle says he was happy with his side’s showing.
“I think first half was flattering with two free kicks and a goal that was questionably offside, and we had three golden chances which we didn’t take later on, but it was good,” he said.
“We’re disappointed in how each of the three goals were conceded, especially the third, but overall, I’m pleased with how we played.
“We know about Tyrese (Sinclair) and his capabilities. We had him with us two seasons ago where he only lasted five minutes in a game up at Gainsborough Trinity, but we know how well he’s done at Mansfield.
“We restricted them to half-chances in the second half. Adam (Collin) made a great save just after the break, but apart from that I don’t think Mansfield offered too much and, in the end, I was really happy – we got through unscathed, which is always nice.
“It was always going to be our toughest game, physically, because of the squad they brought across to us tonight and we’re very grateful for Nigel, Richard (Cooper, academy manager) and Mansfield for that.
“We’re trying to get minutes into the players and remind them to stick to our plan which we did in the end. I thought we looked fit - we got a lot of players through the 90 minutes, which was our primary target tonight.
“The results are irrelevant. Whether we had won or lost tonight, the plan stays as is,” Chettle added. “It’s all about minutes and people playing in their positions and working toward the Scarborough fixture on the 14th.”
Sinclair – son of former Chelsea and Jamaica defender Frank – always looked threatening and may have given Town an early advantage but was denied by Adam Collin, who saved low to his right.
Niall Towle and Matt Thornhill both went close for the hosts in quick succession, but it was Sinclair, felled by the returning Stef Galinski in the build-up, who calmly passed home the resultant free kick after 27 minutes to give Mansfield the advantage.
Minutes later, Sinclair was again bundled over – this time by Dom Roma – and the 20-year-old curled another sumptuous set-piece around the wall to double the arrears, leaving United already staring at a first pre-season defeat.
And it was all but confirmed just before the break when Notts County loanee Knowles raced down the right and found Caine, fresh from signing his first professional contract recently, who slid home Town’s third.
The home side offered little in response but did trouble Owen Mason in the visiting goal on the stroke of half time when James Clifton’s cross-cum-shot was fumbled by the ‘keeper before pouncing on the loose ball under Marcus Marshall’s pressure.
Rev James’ introduction on the hour sparked some urgency but it was Sinclair who nearly notched his hat-trick, only to be foiled by the official’s far-side flag, before James went close to sealing a consolation for United late on but was just out of reach of Alex Howes’ cross.
United face Newark FC in their penultimate pre-season fixture on Saturday, July 31 before a trip to Nuneaton Borough a week later rounds off their preparations ahead of the Northern Premier League opener.
On current fitness levels, Chettle said: “Stef returned tonight after he had a sore back. We took him out of training as a precaution, as was the case with Dom who had a sore ankle so had a week off after the Long Eaton game.
“Callum (Chettle) is hopefully being sorted out this week after he had a scan on a knee problem. Ollie Clark is long-term; we know about his ACL, but Ryan Wilson and Kane Richards should both be okay for the start of the season.
“We are getting people back, but we just need to monitor them throughout the week and hopefully they get some more game time in our remaining pre-season fixtures before the first league game.
“We prepare for that game with the group that we have. I will always say that you go as strong as you can at all times and we can’t rely on the kids all season,” he mentioned, when discussing season preparations.
“There will be times when we need to draw on them and how well they’ve done and again they’ve shown tonight how good they are.
“Jordan Haywood has played against both Forest and Mansfield in the space of a week, which is great for his development, but Ryan Wilson will remain my first choice left-back.
“But it doesn’t give me a selection headache, more piece of mind that we can call on them should something happen to anyone else.”
BASFORD UNITED (from): Adam Collin, Dom Roma, Brad Gascoigne, Stef Galinski, Jordan Haywood, Declan Dunn, James Clifton, Alex Howes, Matt Thornhill, Niall Towle, Marcus Marshall, Jordan Pierrepont, Wayde Hines, Rev James, Nathanial Peters, Ferdinand Bartley, Kiarn Nyemba, Sam Newell, Josh Timson
MANSFIELD TOWN XI (from): Marek Stech, Owen Mason, James Clarke, George Cooper, Ryan Burke, Corey O’Keefe, Taylor Anderson, Jason Law, Keaton Ward, Trialist, Jordan Bowery (c), Tyrese Sinclair, Nathan Cain, Jimmy Knowles, Jack Deakin
MATCH ATTENDANCE: 327