Gloucestershire 337 and 99 for 3 lead Lancashire 402 (Croft 80, Wood 50, Higgins 3-55) by 34 runs
Croft was dismissed for 80 and Wood 50 as the visitors extended their first innings total from an overnight 226 for four to 402 all out, a lead of 65. Ryan Higgins claimed three for 55.
By the close, Gloucestershire had struggled to 99 for three in their second innings, just 34 in front, with Miles Hammond unbeaten on 25. But rain is forecast tomorrow and could come to their aid.
The day began with Croft one short of his fifty, which came up with a two off Matt Taylor in the second over, It had occupied 112 balls and featured seven fours.
Hopes of a Lancashire acceleration dipped when Phil Salt, having added just five to his overnight score of 33, aimed a loose drive at Tom Price and was pinned lbw on the back pad.
George Balderson helped Croft add 48 for the sixth wicket in just under 15 overs before the latter fell to the second new ball, edging a drive off Ryan Higgins through to wicketkeeper James Bracey.
Croft had faced 154 balls and extended his boundary count to 11. With only seven runs added, Balderson, on 20, fell in similar fashion to another outside edge, giving Higgins his third wicket.
At 289 for seven, Lancashire were still 48 runs behind. But Wood brought up the 300 and a third batting point with a pulled four off David Payne.
By lunch, the score had progressed to 317 for seven and the afternoon session saw Wood and Tom Bailey continue a profitable partnership.
They had added 67 to put their side in front by 19 when Bailey, who had taken the dominant role with 8 fours in his 40, fell leg-before to a delivery from left-arm spinner Zafar Gohar, which drifted in.
By then, Lancashire had settled for three batting points and were intent on building a meaningful lead.
Will Williams contributed 12 to another useful stand of 43 with Wood before being caught at cover off Payne.
Wood went to his half-century off 108 balls, with seven fours, but perished soon afterwards, lofting a catch to deep mid-wicket off Payne, who finished with three for 81.
Price had figures of three for 80 in a Gloucestershire seam attack, who bowled wholeheartedly and without much fortune on the slow pitch.
The hosts reduced the deficit of 65 by 20 in their second innings before George Scott edged Bailey and fell to a slip catch for the second time in the match.
It said much about the surface that Lancashire turned to the spin of Jack Morley after only 11 overs, five of which had been sent down by Williams as a cost of only a single.
But it was another seamer, Balderson, who made the second breakthrough when Glenn Phillips, on nine, shouldered arms to a ball that nicked his off stump.
First-innings centurion Chris Dent looked in control again, moving to 23, but then edged a defensive shot off Williams to wicketkeeper Salt to put his side in peril at 73 for three.
The light was poor in the closing overs, which may have explained why Bailey switched to off-spin as Hammond and Bracey saw Gloucestershire to the close.