Keedy has been taking dozens of wickets for the second team since his last championship appearance against Middlesex at Uxbridge in the first week of July.
``He has been bowling well and he deserves his chance,'' said Watkinson.
The 22-year-old, signed from Yorkshire three years ago, is set to be offered a new contract by Lancashire after the committee meeting tomorrow night.
Mike Atherton returned in place of Jason Gallian in the other change from the team which drew with Yorkshire last week.
Essex had skipper Paul Prichard and former Lancashire all rounder Ronnie Irani back from injury as they prepare for this weekend's NatWest Trophy final.
Play on all four days will still start at 10.15am with the game finishing by 3.25pm on Friday afternoon, even though Essex now have an extra day to prepare for the Lord's showpiece which has been put back to Sunday because of Saturday's funeral of Diana, Princess of Wales.