America moved to the top of Group 4 as Jimenez struck twice in their 3-0 win at home to Panama's Sporting San Miguelito.
The 22-year-old striker turned provider in the 80th minute when he set up Andres Andrade for the sealer at the Estadio Azteca.
Jimenez opened the scoring five minutes before half-time, finishing a Rubens Sambueza cross into the roof of the net, and his second goal on 77 minutes came in similar fashion, although the cross was delivered from the right hand side by Paul Aguilar.
The Mexican side had plenty of success from wide areas and the third goal again came from a cross.
Jimenez was unable to apply the finish but played a pass to Andrade, who swivelled before placing his effort into the bottom corner.
The Panamanians are bottom of Group 4, while Alajuelense are second, three points behind America but with a game in hand.
San Jose Earthquakes recorded their first win in Group 5 with a 3-0 victory at home to fellow MLS outfit Montreal Impact.
Chris Wondolowski, Marvin Chavez and Shea Salinas scored in the comfortable win at Buck Shaw Stadium.
Sporting Kansas City missed a chance to take complete control of Group 2, held to a 1-1 draw at home to Nicaragua's Real Esteli.
Jacob Peterson cancelled out Rodel Calero's 54th-minute opener to help the MLS side move four points clear atop the group.