With suspended coach Gerardo Martino watching on from the stands at State Farm Stadium, Mexico were frustrated by the minnows on Tuesday.
They were unable to create much of note through 90 minutes, but found a breakthrough early in extra time through a Jimenez penalty.
After a soft spot-kick was awarded, Jimenez stepped up to send 10-time champions Mexico into the decider.
Mexico struggled to create clear-cut chances throughout the first half as Haiti defended desperately.
Roberto Alvarado fired a decent opportunity wide in the 10th minute before Jimenez put an effort over the crossbar from close range.
Haiti were well-organised and frustrated Mexico, who struggled to put shots on target in the opening 45 minutes.
Jesus Gallardo and Jonathan dos Santos missed the target with efforts, while Jimenez forced a relatively comfortable save from Johny Placide with a 35th-minute header.
Haiti also had their moments, threatening early in the second half as Frantzdy Pierrot fired wide on the turn in the 49th minute.
Andres Guardado was the next to threaten for Mexico, his curling 20-yard free-kick tipped over by Placide, whose last-ditch tackle later denied substitute Uriel Antuna.
Forced to extra time, Mexico finally found their breakthrough in somewhat controversial fashion through Jimenez.
The forward went down in the area under the slightest contact, before stepping up to convert from the penalty spot.
Haiti's brave effort went to the end as they almost stunningly equalised in the 119th minute, Mikael Cantave's 20-yard strike hitting the crossbar with Mexico goalkeeper Guillermo Ochoa beaten, while Luis Montes missed an open goal at the other end.
What does it mean? Mexico's struggles continue
Martino's men looked in fine form leading into the tournament and again to open the Gold Cup. However, they have battled to wins over Martinique, Costa Rica and Haiti in recent matches.
Jimenez delivering for Mexico
The forward was the most threatening for Mexico and won and converted the match-winning penalty for his fifth goal of the tournament. Jimenez has now scored in three straight games for Mexico.
Haiti almost cause a shock
This was quite the performance by Haiti. The minnows, who stunned Canada in the quarter-finals, sat relatively deep and frustrated Mexico for long periods, only to be undone by the extra-time penalty.
Mexico will face either the United States or Jamaica in the final in Chicago on Sunday, while Haiti look ahead to the CONCACAF Nations League starting in September.