Darlington goalkeeper Przemyslaw Kazimierczak thought he had earned his side a point with a point-blank save from Matt Bloomfield in the 74th minute.
But Wycombe found a winner deep into second-half stoppage time when Chris Zebroski fired in from close range to give Wycombe their first win in six games.
After a quiet opening to the game Darlington midfielder Franz Burgmeier tested Chairboys keeper Jamie Young in the 14th minute with a long-range drive that the keeper safely collected and a minute later home striker Danny Carlton fired narrowly wide from ten yards out.
Wycombe responded with a header from Zebroski after 21 minutes that flashed wide and then a low drive from Lee Sawyer was blocked four yards out by Darlington defender Alan White.
Burgmeier sent over a free-kick in the 43rd minute that found the head of Liam Hatch inside the Wycombe area but Young was well-positioned to keep out the striker's effort.
Slack marking by the Quakers defence allowed John Akinde to score in the 39th minute. Darlington failed to clear their lines when defending a corner and, when David McCracken found Akinde six yards out, the big striker calmly fired past Kazimierczak.
Darlington came close to an equaliser in the 48th minute when Young did well to tip a curling free-kick from Burgmeier over the bar.
The home side did draw level in the 60th minute when midfielder Jason Kennedy fired in his first goal since October after the Wycombe defence had failed to cut out Burgmeier's pass.
Bloomfield was denied by Kazimierczak in the 74th minute when his powerful ten-yard drive was turned away by the Darlington keeper and then, deep into stoppage time, a Craig Woodman cross found Zebroski almost on the line and a simple strike earned victory and a valuable three points for the Chairboys.