On a 0-1 pitch, Ludwick hit his first homer of spring, a liner that landed on the grassy berm in left field.
The Reds then added three runs in the eighth with a run-scoring single from Brandon Phillips and a two-run homer by Votto.
The Padres' Opening Day starter, Edinson Volquez allowed just one run and two hits in his five-plus-inning start. But in typical Volquez fashion, he labored with a lot of pitches throughout his final spring outing and walked six while striking out one.
Mike Leake, the Reds' No. 5 starter, completed six innings and allowed one run and five hits with no walks and four strikeouts.
With two outs in the top of the second against Leake, Cameron Maybin hit a single to center field and scored on Kyle Blanks' RBI double off of the wall in right-center field for a 1-0 lead.
Facing Volquez in the fifth with one out, Choo became the first Reds batter to notch a hit with his second homer of the spring, a solo shot the opposite way to left field.
Reds up next: Todd Frazier has four home runs and nine RBIs in his last eight games for the Reds. After a day out of the lineup Wednesday, Frazier will be back Thursday at 4:05 p.m. ET when Cincinnati plays the Royals at Goodyear Ballpark, available on Gameday Audio. Mat Latos will make his final tune-up start.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. This story was not subject to the approval of Major League Baseball or its clubs.