Convey, a former United midfielder, scored on a 20-yard rocket in the 74th minute and Saad converted a one-on-one opportunity against back-up goalkeeper Andrew Dykstra after beating an offside trap.
United (1-2-1 in preseason) will play its group finale Saturday against the first-place Montreal Impact (1 p.m. ET, streaming video on mlssoccer.com).
Ben Olsen fielded a lineup that seems likely to start the March 2 season opener at Houston: Bill Hamid in goal; Chris Korb, Brandon McDonald, Dejan Jakovic and Daniel Woolard on the backline; Nick DeLeon, Marcelo Saragosa, Perry Kitchen and Chris Pontius in the midfield; and Dwayne De Rosario and Lionard Pajoy up front.
In the 31st minute, Robbie Russell and trialist Jan Frederiksen replaced Korb and Woolard, respectively. Trialists Joseph Nane and Kyle Porter entered for Kitchen and Pontius, while 16-year-old homegrown signing Michael Seaton and Honduran trialist Walter Martinez took over on the frontline.
Six minutes later, DeLeon was replaced by Panamanian trialist Marcos Sanchez.
The second half lineup: Hamid (Dykstra 59th); Russell, trialist Henry Kalungi, trialist Shavar Thomas, Fredericksen; Sanchez, Nane (Conor Shanosky 83rd), Lewis Neal (Lance Rozeboom 81st), Porter; Martinez (trialist Ryan Richter 68th), Seaton (Rafael 62nd).
Did not play: Joe Willis (foot injury), Matt VanOekel, Syamsir Alam, Taylor Kemp, Casey Townsend (quadriceps-groin), Ethan White (ankle), Raphael Augusto, John Thorrington.