The Rolex Series was making its return after the coronavirus hiatus but the weather did not roll out the red carpet with rain falling throughout the entire day at The Renaissance Club.
Fleetwood carded a brilliant 69 as he goes in search of a third Rolex Series victory, while Ormsby registered a 70, Kinhult signed for a 71 and Poulter battled to a 73.
Spaniard Adri Arnaus, Frenchman Victor Dubuisson and Malaysia's Gavin Green shared the lowest rounds of the day with a trio of 67s to sit at five under alongside England's Andy Sullivan, who recorded a 69.
Rock is now coach to some of the European Tour's biggest stars but he showed he still has the game that has brought him two victories, including a memorable win at the 2012 Abu Dhabi HSBC Championship, where he held off Rory McIlroy and Tiger Woods on the final day.
He achieved a top five in July at the Betfred British Masters hosted by Lee Westwood and has been trending in the right direction, with only a disappointing third round stopping him from contending at last week's Dubai Duty Free Irish Open.
Overnight leader Lucas Herbert made a bogey-bogey start to put Rock into a one shot lead and, while the Dubai Desert Classic champion responded by taking advantage of the par five third, so did Rock to keep his nose in front.
Poulter spun an absolute stunner of an approach to close range on the fifth to get to double figures and produced more wonderful iron play to get up and down on the par five seventh and join the lead.
He made a gutsy par save after a poor tee shot on the eighth and needed another clutch putt to stay at 11 under on the tenth before hitting the pin to save another par at the next.
The run of saves ended after a poor tee shot on the 12th but he was soon back in a share of the lead as Rock found a nasty lie to drop a shot on the 11th.
The leaders were moving backwards and Rock failed to get up and down on the 13th before Poulter missed a short putt on the 14th and failed to make par from sand on the next for back to back bogeys.
Another bogey from Poulter on the last then meant Rock opened up a two shot lead as he parred his way home.
Fleetwood birdied the par five third and seventh while also picking up a shot on the gettable fifth but he bookended that run with dropped shots on the second and eighth.
A three putt on the par five tenth and missed putt on the par three 12th after a beautiful tee shot represented missed opportunities and it looked like he may be made to pay after a bogey on the 13th.
But another sensational tee shot into the short 14th brought a birdie and a wonderful approach to 15 feet on the last left him well in contention.
Ormsby dropped a shot on the second but flew up the leaderboard with birdies on the third, fifth, sixth and tenth before dropping shots on the 12th and 15th in the worsening conditions.
Kinhult's six birdies were a very impressive return but he cancelled them out with six pars and six bogeys, including three in a row from the 12th.
Home favourite Robert MacIntyre carded a 68 to sit in a group of 12 players at four under including fellow Scotsmen Grant Forrest and Marc Warren, and Rolex Series champions Brandon Stone and Lee Westwood.