Mark Jackson took charge of a young squad at Nethermoor Park with senior boss Marcelo Bielsa in attendance in LS20.
There was a Whites debut for winger Amari Miller while midfielder Adam Forshaw was a second half substitute as he continues his comeback from long-term injury.
Tricky wide man Crysencio Summerville won a penalty and hauled himself up to convert from the spot to open the scoring for the visitors.
The Lions, though, hit back three minutes later as Kaine Felix found Bailey Thompson in the box to level.
United went back in front before the half-time interval thanks to an impressive Sam Greenwood free-kick after the former Arsenal youngster continued his stunning set-piece form in front of goal.
A competitive second half played out before Leeds thought they had wrapped up victory as Summerville turned provider for midfielder Charlie Allen.
Guiseley though, again hit back within seconds of the restart through Lewis Hey to ensure a nervy finish - but the Whites held on for victory.
United's more senior players will be in action against Blackburn Rovers at Ewood Park on Wednesday night while games against Fleetwood Town and Real Betis are pencilled in for later this week.
Here, we take a look at some of the best pictures from Nethermoor Park as Leeds made a winning start to pre-season...