The Fightin Phils blew leads in the ninth and 12th innings in an 8-7 loss at Harrisburg Thursday night.
Reading built a 4-0 lead, then led 5-2 heading into the ninth inning.
But the Senators scored three times in the ninth to force extra innings.
The Fightins then scored twice to take a 7-5 lead in the 12th, only to see the Senators score three times in the bottom of the 12th to win it.
Jay Johnson (0-2, 13.50) blew the save and suffered the loss on the mound.
Aaron Altherr, Logan Moore, and Carlos Alonso all had three hits to pace the Fightin Phils offense.
Reading (30-27) will return to Baseballtown to open a seven-game homestand Friday night against Richmond.