Spears delivered career highs with two homers and six RBIs before Rizzo collected his 29th RBI in August in Double-A Portland's 10-5 win over Harrisburg.
Spears ripped a two-run drive to right field, his 16th of the year, off Senators starter and former first-round pick Aaron Thompson in the first inning. He struck again with a three-run drive in the second off Thompson, also to right. He added an RBI single in the fifth.
The 25-year-old has made his hits count lately -- he has just eight hits in his last 10 games, but he's managed to hit five homers and knock in 12 runs in that span. He has 22 RBIs on the month.
The Fort Myers, Fla., native easily surpassed his previous high of four RBIs in a game, which he most recently posted July 9 against New Britain.
Rizzo's three-run double in the fourth gave the first baseman 29 RBIs in August, the most for any month in the 17-year history of the Portland franchise.
Despite setting the club mark, the 21-year-old entered the game hitting .206 in his last 10 starts. A two-homer, five-RBI night Aug. 19 helped keep him on pace to set the record.
Aaron Bates (2009), Ross Gload (2000), Kevin Millar (three times in 1997) and Jon Still (2009) held the previous record of 28 RBIs in a month.