Three Liam Norwell wickets ignited Gloucestershire’s chances of a final-day push for victory at Worcester.
The visiting seamer took 3-28, bowling first-innings centurion Tom Kohler-Cadmore, as the hosts stumbled to 151-5 in their second innings to lead by 226.
Rain curtailed play at 16:40 BST, but all three results are still possible.
Earlier, Graeme van Buuren carried his overnight 104 to 172 not out, in tandem with Craig Miles (60 not out), as the visitors declared on 364-6.
Gloucestershire caused a surprise by pulling out at lunch still 75 runs behind after the unbroken 134-run stand between Van Buuren and Miles.
Worcestershire captain Daryl Mitchell told BBC Hereford Worcester:
“The game has opened up with them declaring. It was a good move. Hopefully that will create something exciting.
“We are all sick of boring draws, so let’s hope we have got a game of cricket on.
“The closer they got to our total, it would have made it more difficult to play a proper game. We’ve got to start trying to win and they are in the same boat.”
Gloucestershire head coach Richard Dawson:
“We’ve got five wickets down and if we can get a couple of early wickets, we will put the pressure back on them.
“Was the declaration on the spur of the moment? We had to see how we batted. And Graeme van Buuren and Craig Miles put us in a position where we could make that decision.
“The partnership they put on actually put us into a position where we could dictate things.”