After posting a first innings total of 384, Durham restricted Somerset to within 27 runs of their total with two wickets remaining by the close of play on day two.
Durham began the day with the total at 353-8 with Liam Plunkett and Jamie Harrison returning to the crease.
Harrison was caught by Alex Barrow off Trego for 15, adding 12 runs to his overnight score. Four well placed boundaries from Liam Plunkett saw him reach 24 before he was caught behind off Thomas, ending Durham’s innings with the score at 384.
Harrison opened the Durham attack and struck in his second over, trapping Arul Suppiah lbw on 4.
Stephen Harmison struck in the over after lunch when Barrow was caught behind on 25 with the Somerset total at 66.
James Hildreth struck a speedy 35 ball fifty, as part of a 72 run third wicket partnership, before he was bowled by Harrison on 53.
Somerset were 203-5 after Ian Blackwell struck in consecutive overs, with Nick Compton caught at mid wicket by Callum Thorp on 64 and Buttler caught behind without scoring.
Craig Kieswetter looked pretty frustrated when he was trapped lbw on 42 the following over.
At one point Craig Overton and Trego put on 55 runs from seven overs, with the youngster reaching his fifty fairly swiftly before the 99 run partnership was brought to an end when he was caught behind off Harrison, becoming the debutant’s third victim of the innings.
Trego passed fifty fairly slowly with support from Alfonso Thomas, who became Blackwell’s third victim when he was caught by Ben Stokes on 18 with Somerset 46 runs behind Durham’s first innings total.
At the close of play Somerset were 357-8, with Peter Trego 67* and George Dockrell 3* and trailing the Durham total by 27 runs.
Durham TV spoke to Jamie Harrison about his debut, keep an eye out for that interview on Thursday.