Rotherham survived a spirited second-half comeback from the Cornish Pirates to take the spoils at Clifton Lane.
The home side led 19-0 on the hour mark, all their points coming from fly-half Juan Pablo Sacino who picked up a try and four penalties.
The Cornish side then sprung into life, as two Rob Cook penalties and a Wes Davies try closed the gap to 19-13.
The Pirates kept pressing and were rewarded with a penalty try, but Cook missed the conversion to win.
The result ended the Pirates' six-match winning streak, and gave Rotherham revenge for the 40-15 defeated they suffered at the Mennaye Field last October.
Rotherham were by far the stronger in the opening exchanges, four penalties from Sacino putting them 12-0 ahead at the break.
Sacino continued to rack up the points in the second-half, scoring and converting the game's first try after 13 minutes, as he intercepted a loose pass to run the ball in from half-way.
With the game looking out of reach at 19-0, two Cook penalties brought the Cornish side a glimmer of hope, that grew further when Davies squeezed over in the corner with 17 minutes left to play to put the score at 19-13.
The Pirates proceeded to throw everything at Rotherham, and after several scrums just in front of the home side's posts, were rewarded with a penalty try.
Cook's conversion from in front of the posts to give his side victory looked routine, but Rotherham's defence, alert to its significance, charged the kick down to ensure the points stayed in Yorkshire.
Cornish Pirates backs coach Harvey Biljon told BBC Radio Cornwall: "I'm pretty disappointed, and I think if you look at the players they're pretty unhappy themselves.
"We worked hard, but I also think we need to learn to stay composed, build the phases and that pressure will turn into points.
"The (Rob Cook's) conversion is just one of those things, but I don't think it would have gone over if they didn't charge it down."
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