Gloucestershireshire 356 and 137 for 5 (Marshall 43*, Footitt 2-29) lead Derbyshire 372 (Madsen 80, Chanderpaul 73, Howell 4-68) by 121 runs
Hamish Marshall holds the key to Gloucestershire's chances of avoiding defeat by Derbyshire on the final day at Cheltenham.
Marshall, the experienced former New Zealand Test batsman, was unbeaten on 43 at the end of day three, with his side 137 for 5 and leading by a precarious 121 on a pitch that has offered assistance to the bowlers throughout.
An advantage of 200 would give the hosts a sporting chance. Marshall and Will Gidman, with 39, showed what was possible with a stand of 81 in the final session after their team had been reduced to 40 for 4.
Earlier, Derbyshire extended their first innings total from an overnight 216 for 3 to 372, Wayne Madsen falling for 80, while Shivnarine Chanderpaul contributed 73 and Wes Durston 58. But it could have been so much better for the visitors, who lost their last five wickets for 12 runs as medium pacer Benny Howell picked up 4 for 68 from 24 overs, having been unusually selected for new ball duties.
Derbyshire looked to be moving into a commanding position in the morning session, despite losing skipper Madsen to a gully catch by Will Tavare off Howell, having added only one to his overnight score.
A fluent 49-ball half-century from Durston built on the good work of Chanderpaul, who had made 73 when brilliantly caught by second slip Michael Klinger, diving in front of first slip, with Will Gidman the successful bowler. Durston looked in prime form from the start of his innings and helped take Derbyshire into the lead, striking 10 fours and a six before offering a catch to backward point, accepted by Marshall diving forward.
At 360 for 6, the visitors still looked poised for a meaningful first innings advantage. Instead, Howell and off-spinner Jack Taylor mopped up the tail in the space of seven overs to put Gloucestershire right back in the game.
The pitch continued to offer assistance to seam and spin, so the hosts knew they would face a testing spell against the new ball at the start of their second innings. So it proved as first innings centurion Tavare edged left-armer Mark Footitt to wicketkeeper Gareth Cross without scoring and the dangerous Klinger carelessly square drove a catch to point off the same bowler when on 13.
Tom Taylor forced Alex Gidman to edge onto his stumps and Tony Palladino achieved a similar result against Ian Cockbain as the home side found themselves only 24 ahead with four top order batsmen back in the pavilion.
But Will Gidman is in the batting form of his life and was soon counterattacking with the aid of Marshall as some of the shine and hardness went out of the ball. The pair capitalised on anything loose and Gidman launched David Wainwright over mid-wicket for six as the total went past the 100-mark.
Durston broke partnership with his offspin by having Gidman caught at slip pushing forward and all results remain possible on day four.
"We believe a 200 lead would give us a good opportunity to win because the wicket is starting to turn more and the new ball has nipped about in each innings," Will Gidman said.
Derbyshire's Durston added: "It's going to be an interesting final day. We aren't setting ourselves targets, but we need to get Marshall early as he has played well for a couple of hours. If we can open up that end and bowl well in the morning we will give ourselves every chance.''