The Bees established a 2-0 half-time lead before allowing the Championship side a goal back.
"Generally we played a good game," added Frank. "We controlled the game in and out of possession in the first half and created a lot of chances and pressed with intensity.
"In the second half we became a tiny bit sloppy, but all in all a it was a very good away performance against a good side. I'm very pleased."
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