Rowbottom sped to his and his DRM team’s second win in three races in the first of two rounds at the Northants circuit.
But in the second encounter he struggled to a lowly 15th place and just one point after car set-up issues on a greasy damp track.
It meant that having slashed the gap to championship leader Max Coates from 70 points to 42 in race one, Rowbottom, fourth in the standings, left Rockingham some 61 still behind.
A maximum of 112 points is available from the remaining four rounds at Silverstone and Brands Hatch.
“The win was great but for the second event in a row I found myself coming away really frustrated – win race one; then a nightmare in race two,” explained Rowbottom.
“It was the same a fortnight before at Snetterton. Both there and Rockingham have been like a game of snakes and ladders with us climbing high but then sliding back down almost to where we started.”
Rowbottom’s second race was made worse by a collision with WDE’s Nic Hamilton, but he is confident he will be on race-winning form when the season continues at Silverstone in mid-September.
“The car took quite a big knock – it was just one of those unfortunate things but it means we have some repairs to do,” added Rowbottom. “I also woke up with some sore ribs on Monday – actually I have to say the Clio Cup car helped protect me really well from what was quite a big impact – but otherwise I’m OK.
“So now Silverstone and Brands Hatch… 61 points from four races is a bigger ask than 70 from six races which is what it was before Rockingham.
“But I am sure we will be in a very strong position and can win both races at Silverstone – I’d love to join the list of drivers who’ve done the double.
“Mathematically I need to be within 55 after Silverstone to stand any chance at Brands although realistically I accept that could do with being below 30.
“But so long as the maths still say there is a chance then 100 per cent I will not give up. I’ve nothing to lose.”