On day three of their Vitality County Championship match against Derbyshire, Glamorgan took the lead by posting 361 for seven declared, setting a target of 401 for the visitors.
Chris Cooke was the mainstay for Glamorgan, finishing on 126 not out, which is by far the highest score of this match so far. He received good support from James Harris, who scored 61 not out, and Dan Douthwaite, who made a well-crafted 32.
In the 12 overs bowled before close, Derbyshire reached 40 for one with David Lloyd and Luis Reece remaining unbeaten.
As Derbyshire still requires 361 runs to reach their victory target, a Glamorgan victory is the most likely outcome as the match heads into the final day with a mixed weather forecast.
Mason Crane came in as a nightwatchman late on day two and supported Colin Ingram in a 45-run partnership for the fifth wicket. Crane was trapped lbw by Thomson for 19, bringing the experienced pair of Ingram and Cooke together. Batting started to look straightforward for the first time in this match.
Ingram batted with great rhythm, passing fifty from 76 balls. Shortly after reaching the milestone, he called Cooke through for a single but was sent back too late and was run out by a throw from Sam Conners.
In the first two innings of the match, wickets had fallen quickly at this point. Cooke and Douthwaite formed a partnership worth 109, the highest of the match up to that point. Cooke, who missed out on batting during the record-breaking efforts at Lord's last week, made the most of his opportunity in this game, scoring the 13th hundred of his first-class career.
After the ball spun considerably in the first two days, it was easier on day three, but Thomson remained a threat. He bowled the first 33 overs of the Glamorgan innings from the River Taff end and sent down 44 overs in total, finishing with career-best match figures of 12 for 201.
Cooke was joined by Harris after Douthwaite was dismissed by Thomson to complete his second five-wicket haul of the match. Glamorgan continued to dominate with a second consecutive hundred-run partnership, surpassing the previous stand by Cooke and Douthwaite, reaching an unbeaten 116 for the eighth wicket. The declaration set Derbyshire a target of 401.
Harris was the only one to take a wicket on the third evening, dismissing Harry Came for three with an lbw. As the clouds covered Sophia Gardens in the early evening, play was suspended due to darkness with three overs remaining.
The outcome of the match will largely depend on Crane's performance on the final day, as the ball is still turning on this pitch and Glamorgan needs nine wickets for victory.