Off-key United took until just before half-time to break down some stubborn resistance by struggling Boro, who thought they had salvaged a late point courtesy of Francois Zoko’s 86th-minute leveller.
Stevenage goalkeeper Chris Day denied Alex Revell after 20 minutes, tipping his shot over the crossbar, but Stevenage finally cracked five minutes before the break.
Shots by Kieran Agard and Wes Thomas were blocked on the line, but the ball ran loose to Mark Bradley and he whipped in a hard, low cross which Thomas turned into the net, with referee Scott Mathieson waving away the visitors’ offside claims.
Rotherham almost doubled their lead after 54 minutes but a great save by Day denied Revell.
And then with just four minutes remaining, from Boro’s seventh corner of the second half, Jimmy Smith’s corner was flicked on by John Mousinho and Zoko crashed the ball home at the far post.
But just two minutes later Rotherham hit back. Substitute Haris Vuckic held the ball up on the edge of the penalty area and slipped a pass to Frecklington, who drilled his shot into the bottom corner.