Saints go into Monday night's game at McDiarmid Park four points ahead of their Tayside rivals but they have been unable to gain the upper hand on the pitch since their return to the Clydesdale Bank Premier League.
Lomas said: "Them and Motherwell have probably been the two teams that we haven't done great against. It would be nice to address that on Monday.
"But they have a lot to play for themselves and have some decent players.
"They beat us 5-0 last season but apart from that it's been pretty tight, a goal here or there and we expect more of the same.
"We have had a couple of draws already this season so it shows the teams are evenly-matched."
Saints last played on March 9 and their break has allowed Gary Miller and Tam Scobbie to overcome ankle injuries, while the likes of Frazer Wright and Steven Anderson have rested niggling injuries.
But Lomas is unsure how the 23-day break will affect his team's performance.
"You only look at it as a positive if you win when you come back," he said. "If you win it, you think those three weeks were great and if you lose, you think they were a nightmare.
"Right at the start we gave them a few days off and last week we had five days on the spin training, which was like a mini pre-season. This week has been more like a normal week, albeit the game is not until Monday."