Pompey's four-match unbeaten run came grinding to a halt after Billy Bodin's first-half strike secured a 1-0 win for the Gulls.
Barker's side now find themselves just three points clear of the drop zone ahead of next weekend's trip to Exeter.
"We've got work to do all over the park, so we'll crack on with things again," said Barker.
"But we certainly never got carried away by the improved recent run. This has put us back in it again."
- Sports & Recreation
- Billy Bodin