The weather gods smiled on Lancashire as play began under clear blue skies with the sun shining. It looked ideal batting conditions and there were few alarms for Jennings and Jones as they built on a stand that had reached 29 by close of play on day three.
Jennings slashed the first boundary of the day through cover off Matt Taylor and Jones soon showed positive intent too, hitting the left-arm seamer for successive boundaries in the fifth over of the day.
Gabe Bell bowled a tidy spell from the Ashley Down Road End, but when he was replaced by Will Williams another Jennings boundary took the runs needed to below 100.
Gloucestershire made a breakthrough in the 13th over of the day when Jones played defensively to a ball from former Lancashire seamer Williams that left him and edged to second slip where Cameron Bancroft took a comfortable waist-high catch.
At 121-4, Lancashire required a further 81 runs, with Jennings a reassuring presence in the middle. But Gloucestershire thought they had him caught behind off Henry Brookes with the score on 125, but umpire Ian Blackwell had signalled a no-ball.
Soon afterwards, Jennings completed a 138-ball half-century including eight fours. But he lost another partner with the total on 143 as Matty Hurst, on eight, miscued an attempted shot through the leg-side off Bell, who had switched to the Pavilion End, and was caught at mid-wicket.
If Gloucestershire sensed a chance, it was snuffed out by Arav Shetty, who provided positive support for Jennings in a match-clinching stand, which had added 45 precious runs by lunch, taken at 188-5, with only 14 needed and the hard work done.
Still Gloucestershire refused to surrender and the second over after the interval saw Shetty bowled by off-spinner Ollie Price with 10 still required. George Balderson was almost run out taking a quick single to get off the mark, just making his ground at the bowler’s end.
A Jennings boundary to fine leg off Price calmed any nerves and four byes down the leg side ended the match at just before 13:55 BST.
It was a contest several seam bowlers could look back on with pride. Lancashire’s Balderson and James Anderson had match figures of 9-109 and 7-63 respectively, while Gloucestershire Matt Taylor returned 7-105.
The visitors had every cause for satisfaction at a solid all-round performance marred by the serious injuries to Ajeet Singh Dale (hamstring) and Luke Wells (dislocated shoulder), while Gloucestershire could take some consolation from being a lot more competitive than in their opening two Championship fixtures, which both ended in innings defeats.