Mitchell-Thomas had a third and a second behind Summers at Hampton, while a crash on the first bend in race one was not an ideal start to Dibben's drive to defend his 2012 super moto title.
"My front wheel just went from under me and I slid," Dibben said yesterday.
Apart from his pride, Dibben suffered no injuries and climbed back in his scooter to claw his way through a field of more than 20 riders to take fifth.
"The second race was a bit better and I had a real battle with Jayden Carrick [Wanganui] and Duncan Hart from Tauranga, but I managed to keep them at bay to run third behind Toby and Mal," Dibben said.
"Mal had a good day and got a real feel for New Zealand race conditions which are a bit different to what he's used to, but he handled it well and I'm sure he will enjoy the flat surface at Manfield this weekend."
Mitchell-Thomas heads to Manfield in second place, nine points behind Summers, while Dibben is tied for fourth.
The Brit has an interesting road ahead, especially when he lines up on the grid in Wanganui on Boxing Day. He has never raced on a street circuit.
Supermoto series points: Toby Summers, 51; Malachi Mitchell-Thomas, 42; Duncan Hart, 37; Richard Dibben, 36; Casey Bullock, 36; Aden Brown, 28.