In the third inning, O'Neill hit a two-run shot over the right-field wall that tied the game at 3. It was his AFL-leading third homer.
"I was looking up at the ball, just being hopeful and it eventually carried out," O'Neill said. "If we can tie the ballgame up early, we've got a pretty good chance in the end."
This was O'Neill's second straight game with a home run, after hitting 24 home runs and 102 RBIs this season for Double-A Jackson.
"Obviously everyone loves hitting home runs," O'Neill said. "So I'm just trying to keep doing me out here and hopefully more to come."
O'Neill also walked and scored in the eighth, coming home on a triple by Rays' No. 15 prospect Justin Williams.
"I saw it shoot the gap, so I got on my horse and got home," O'Neill said.
Marlette, who hit .277 for Class A Advanced Bakersfield and Double-A Jackson this season, hit a leadoff double to center field in the seventh inning.
"I was just up there trying to make a good swing on the ball and get a good pitch to drive and swung through the first one," Marlette said. "I kind of just sat back a little more and stayed short and just found the barrel."
After advancing to third on a flyout by Mariners' No. 3 prospect Drew Jackson, a fielding error by White Sox prospect Trey Michalczewski allowed Marlette to score and give Peoria its first lead of the game, 4-3.
"Our third base coach just kept reminding me of the situation and to just let my instincts play it out," Marlette said. "We were going on contact at third, so just put the pressure on them and they couldn't field it."
Marlette picked up an RBI in the eighth inning on a sacrifice fly to center field, letting Rays' No. 15 prospect Justin Williams score.
Also representing the Mariners was pitcher Luiz Gohara, who earned the win after relieving Rays' prospect Greg Harris for the seventh inning. Gohara, Seattle's No. 5 prospect, was one of five pitchers for Peoria who were responsible for tossing six scoreless innings.
"I think we all settled in," Marlette said. "Every pitcher came in and threw strikes and threw their fastball where we needed it to be."