Bale struck in first-half stoppage-time to cancel out Fred Onyedinma's goal as Spurs made hard work of beating the Championship's basement club at Adams Park.
Starting for the first time this year, Bale missed three big chances in the first 30 minutes before beating the offside to turn home Lucas Moura's cross from close range.
Bale also scored against Championship opposition on his last start, setting Spurs on their way to victory in the Carabao Cup quarter-final at Stoke with a deft header, and his latest goal was another reminder of his quality and decisiveness in the penalty box.
â€” Emirates FA Cup (@EmiratesFACup) January 25, 2021
He also betrayed his lack of sharpness by missing a succession of chances, including two in the second half as Spurs laid siege to the Wycombe goal in search of a winner.
Nonetheless, this was an encouraging performance from the Welshman and his most influential since returning to Spurs on loan from Real Madrid in September.
For the first time he completed 90 minutes, suggesting his fitness is gradually getting there, and the 31-year-old looked a constantly threat in the final third.
He should have given Spurs the lead after four minutes but headed Lucas Moura's corner wide before firing two efforts inches past the post, the second after a purposeful run into the box.
Mourinho has consistently warned that Bale is a "different" player to the explosive forward who left Spurs for Real Madrid, and this game offered good insight into the strengths of the "new" Bale.
He came alive in the width of the penalty area, again showing a poacher's instinct for his goal, but often operated a deep-lying playmaker, using his wand of a left-foot to switch play and look for gaps in the Wycombe defence - much like James Rodriguez has done for Everton, who await Spurs at Goodison Park in the fifth round.
Spurs are sorely missing both goals and midfield creativity, and Bale could offer both in the second half of the season â€“ starting against Liverpool on Thursday.
Provided he can stay fit and find a rhythm, some of Bale's old explosiveness will surely return, too.
For Spurs and Bale, the hope is that this game was a turning point in his season.
Spursâ€™ second string struggles
Mourinho made 10 changes from the win over Sheffield United eight days ago, leaving out all his stars including Harry Kane, Heung-min Son and Ndombele.
The result was a dominant performance, but a worrying lack of a cutting edge until the trio came off the bench in the second half.
Carlos Vinicius, who scored a hat-trick against eighth-tier Marine in the last round, was barely involved and offered next to no goal threat. He was predictably hooked for Kane before the hour.
Erik Lamela and Lucas, meanwhile, were lively and tenacious but rarely looked like being the ones to make the breakthrough â€“ even if Lucas' excellent pass set up Bale's goal.
Although the entire second half was essentially a contest between attack and defence, it was not until the introduction of Kane â€“ and then Son and Ndombele 10 minutes later â€“ that Spurs really looked like scoring a winner.
Meanwhile, Mourinho's second-string defence also endured another bad day at the office, with Davinson Sanchez, Toby Alderweireld and Ben Davies all culpable in the build-up to Wycombe's goal. Japhet Tanganga, meanwhile, was replaced by Pierre-Emile Hojbjerg at half-time after offering limited attacking threat from right-back.
Mourinho's reliance on a core group of 14 or 15 players only seems to be growing with every game, which is something of a concern given the barrage of fixtures around the corner with the restart of the Europa League next month.
In the short-term, at least, the majority of Tottenham's XI against Liverpool on Thursday will have essentially had 11 days of solid rest since the win over Sheffield United on January 17, which could give Spurs a significant advantage against Jurgen Klopp's faltering champions and prove beneficial later in the season.
Watch: Warm up routine