The team called up the righthander from Lehigh Valley. Thompson had a 5.36 ERA with the IronPigs.
The hot-hitting Astros are "as good a team as we've seen," Phils manager Pete Mackanin says.
A rain delay lasted nearly two hours. Velasquez could not last after that against his former teammates.
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The Phillie Phanatic may be the best, but he wasn't the first.
The outfielder's return to the Phillies is still ahead of schedule, but he will not be activated Tuesday when he is eligible to return from the disabled list.
Klentak didn't appreciate a question about moves the Phillies might make before the trade deadline.
Howie Kendrick and Pat Neshek continued to enhance their trade value Sunday ahead of the July 31st deadline.
The righthander isn't sure how he will feel on Monday night when he takes the mound against the Astros.
Nick Williams homered and drove in three runs in Sunday's 6-3 win. He is playing like he belongs in the majors.
The game's result - another ninth-inning debacle after a stunning comeback - is less impactful than the performance by Jeremy Hellickson, who failed to showcase himself in the second-to-last-start before the deadline.
Aaron Altherr's strained right hamstring has improved quicker than expected and there is a chance the outfielder could return to the Phillies as early as Tuesday. Altherr has been on the disabled list since July 15 and was expected to miss nearly a month of action.
Reading won its game with a walkoff homer.
The 24-year-old righthander threw 20 more off-speed pitches Friday night, six of them for swings and misses.
The surging pitcher allowed just five hits, struck out nine, walked two and allowed just one run as he logged seven innings for the fifth time in his last six starts.