It was a welcome return to winning ways for the Dons following back-to-back defeats against sides likely to be contesting the honours at the end of the season.
The result was never in doubt against a side put together over the last six months or so but the Dons were made to work harder than they probably expected at times by a side on a steep learning curve.
The Dons had started slowly in their three previous games this season but it took them less than five minutes to open their account.
Stand-off Ben Johnston, playing his last game before a likely suspension, put prop Ben Mathiou into space on the edge of the 20 and the Featherstone loanee held off the cover on an angled run to the line for an unconverted try.
Johnston also set up the Dons’ second try in the tenth minute when he dummied his way into space about 40m out and wrong-footed several defenders before sending full-back Ben Howe over near enough for Connor Robinson to convert.
The visitors hit back in spirited style and reduced the deficit to 10-6 with a 17th minute converted try by hooker Jake Lloyd, who forced his way over from 10m out.
The Dons regained their 10-point advantage when centre Robbie Storey went over from close range.
Cornwall suffered a double blow a couple of minutes later when winger Decarlo Trerise limped off after fumbling a high kick in his own 20 which gifted Storey a second converted try to made it 22-6.
The visitors went close to what would have been a contender for the try of the season on 34 minutes after breaking out of their in-goal area and taking play deep into the Doncaster half before scrum-half Joe Purcell was halted by the cover.
It only proved a stay of execution for the home side, however, with centre Joe Burton rounding off a neat handling move on the opposite flank.
Winger Tom Halliday dived over for another converted try to secure his side a 28-12 interval lead.
Johnston, who must be one of the best stand-offs in the division, scored a well-taken individual try, again converted by Robinson, to open the scoring just after the break.
When winger Travis Corrion touched down for another converted try to make it 40-12 it looked like the floodgates might open.
But it took the Dons until the 65th minute to add to their account with a close-range converted try by prop Keelan Foster during which time the visitors had gone close on several occasions.
Smeaton also forced his way over from close range ten minutes from time but Cornwall had the last word with a last-minute try.
Dons: Howe, Halliday, Storey, Sanderson, Corrion, Johnston, Robinson, Foster, Whitmore, Mathiou, Ollett-Hobson, Smeaton, Peterson. Subs: Fella, Cockayne, Roberts, York.