Stevenson fired us ahead with a well-placed finish prior to half-time, before Howell doubled the lead shortly after the re-start.
The victory strengthens our position on top spot in the Central League (East Division), with just three more matches of the league season to go.
Despite a dominant showing by the Stags, it was Rovers who created the first meaningful chance after just five minutes.
Ben Birch only partially cleared Harry Middleton’s near-post corner, before Lewis Ferguson collected play on the edge of the area and rifled a drive against the upright.
Our side responded with a chance of their own just three minutes later, but Godfrey Poku was unable to test Jon Maxted with a speculative effort from distance.
Maxted also did enough to distract Lindon Meikle, who latched onto Stevenson’s sublime low ball, but blazed over in a one-on-one with the Rovers stopper on the quarter-hour mark.
The Stags slowly started to enjoy a spell of sustained pressure as Rovers were made to defend several set-pieces, and an opener almost arrived on 21 minutes.
Skipper James Jennings flashed a low free-kick into a crowded six-yard box, which ricocheted off Ollie Palmer and drifted narrowly wide of Maxted’s left-hand post.
Moments later, Paul Black also caused havoc with a teasing left-sided delivery that narrowly evaded Palmer, and forced the visitors into more last-ditch defending.
Rovers only caught rare glimpses of the Stags’ goal and after Middleton’s teasing near-post in-swinger was cleared by Keiran Murtagh, Ferguson came no closer with a long-range shot.
Murtagh and Howell both spurned further chances as our team played some excellent football, but were unable to find a way past Donny’s resolute back-line.
However, that changed just five minutes prior to the interval.
Black again tormented his marker on the left -wing and provided a pin-point low cross into the area towards Stevenson, who duly fired beyond a full-stretch Maxted.
The Stags could have doubled their lead within seconds of Donny re-starting play, as Murtagh quickly picked up play and saw his 30-yard strike parried by Maxted.
Palmer was the quickest to react, but somehow the frontman scooped his effort over from the edge of the six-yard box, much to Rovers’ relief.
Meikle then had an effort well-held by Maxted in first half stoppage-time, as the Stags went in at the break with a thoroughly deserved 1-0 lead.
Our team continued to look threatening after the re-start and should have been awarded a spot-kick when Evan Finnegan used his arm to block a close-range effort by Meikle.
Nevertheless, the Stags deservedly doubled their advantage on 52 minutes.
Liam Marsden was the provider as his chipped near-post delivery was flicked on by Palmer for Howell, who spun away from his marker inside the six-yard box and slotted home.
Donny, whose side contained experienced players such as James Harper, Andy Griffin and former Real Madrid star Marc De Val Fernandez, then had a mini-spell of pressure around the hour-mark.
Middleton came close to reducing arrears with a low 20-yard drive that deflected off Birch, and went fractionally wide of Deakin’s right-hand post.
From the resulting corner, Middleton picked out an unmarked Griffin at the far-post, but the veteran full-back blazed his effort into the side-netting.
The Stags then spurned several chances to enhance their winning margin in the last half-hour of the match.
Maxted reacted quickly to palm away Palmer’s header, following a far-post corner by Jennings on 62 minutes, before Howell blazed over on the follow-up.
Meikle was also twice denied by the Rovers custodian, whilst his attempted lob-shot after Marsden’s long downfield ball, fell wide of the target.
Donny almost grabbed a consolation in the closing stages when Chris Whincop flashed a free-kick just wide of the target, from the edge of the area.
However, our second-string were ultimately worthy winners, and stay top of the Central League (East Division) table, with just three matches remaining.
Team: Deakin, Marsden, Birch, Jennings (c), Black, Meikle, Poku, Murtagh, Howell, Stevenson, Palmer. Subs: Fell, Hemagou, J.Thomas, Green, Lamb.