The Rebels went into the game with only one recognised striker due to injury concerns over Brad Wadkins, Chris Flood and Gavin James, so Manny Williams led the line, ably assisted by Lench and Warren Harris.
The visitors wasted little time going in search of the opening goal, and Simon Dunn had already hit a post when Lench headed James Dobson’s free kick past Sam Warrell in the Kidlington goal on seven minutes.
But Kidlington roared back with a strong spell of their own, and Jack Turner needed to make a superb one-handed save, diving to his left to keep out Ben Brown’s header. The hosts then hit the crossbar soon after through Lance Williams, and former Rebels striker Anaclet Odhiambo found himself through on goal by Elliott Osbourne-Ricketts, only to be denied by Turner.
With Kidlington still pressing, Turner also held well after Darius Brown cut in from the left and got a shot in.
Slough survived that passage of play unscathed and the game settled down after an end-to-end start. Williams went closest for Slough, but was denied as Tommy Castle crucially blocked on the line.
Two minutes before half time, Lench won a free kick on the edge of the box from which Slough doubled their lead. Dobson’s effort was saved, with Warren Harris hitting a post on the follow-up – but the ball fell kindly for Lench to finish easily.
Turner made a good save from a Lewis Coyle free kick early in the second half and for Slough, Lench was denied by Warrell and Dobson fired wide.
But the home side carried a goal threat, and Turner made another good save before Odhiambo pulled one back, poking in after Turner had tipped the ball onto the crossbar from Roger James’ swerving shot.
Slough twice went close to restoring their two-goal cushion, with Lench shooting wide and Lee Togwell off target from 25 yards.
But with nine minutes remaining, Lench completed his treble as he slotted into the bottom corner from Williams’ pass. The goal came about as Harris won the ball from Tommy Franklin, who was trying to shepherd the ball out of play.
Williams then added a fourth in stoppage time to seal the win, converting a cross from Harris.
Sam Warrell, Eddie Odhiambo, Tommy Castle (Lewis Coyle 39), Ben Brown, Tom Franklin (c), Lewis Gabbidon, Mark Janes, Elliot Osborne-Ricketts, Anaclet Odhiambo, Lance Williams (Declan Benjamin 86), Darius Browne (Roger James 63). Unused substitutes: Duran Martin, Ryan Wharton.