Pachall managed just 107 yards on 10-of-26 passing in the downpour, but the Horned Frogs (4-0) used five interceptions to nail down their 12th straight victory.
Matthew Tucker scored en route to 56 rushing yards for TCU.
Southern Methodist's Garrett Gilbert had a rough day, throwing five interceptions and completing just 15-of-40 pass attempts. He accumulated 190 yards and a touchdown for the Mustangs (1-3).
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