England hopeful Sam Robson struck an unbeaten century as Middlesex replied strongly to Nottinghamshire's first innings total.
Robson, who combined with Eoin Morgan for a 203 run partnership, finished the day on 144*, with Middlesex on 296/4, 30 runs behind on the second day of the LV=CC match.
While Morgan and Adam Rossington fell in quick succession, John Simpson (32*) joined Robson to see the hosts safely to the close.
Nottinghamshire resumed on 315/8 but only lasted for 4.1 overs on the second morning, as Steven Finn and Tim Murtagh each taking one wicket to bowl the visitors out for 326. Finn's dismissal of Andy Carter meant he completed his second five-wicket haul of the season, finishing with 5/91.
After removing Chris Rogers and Dawid Malan to leave the score at 19/2, Nottinghamshire would have had hopes of bowling Middlesex out cheaply, especially considering the hosts' poor performance against Sussex last week.
But Robson and Morgan combined for a fine partnership, with both hoping to make England's team for the first Test of the summer against Sri Lanka at Lord's in May. When Morgan was caught behind off the bowling of Harry Gurney for 86, Middlesex had moved to 222, 104 runs behind.
Robson and Simpson stood firm, however, and they will resume 30 runs behind and with hopes of building a sizeable first innings lead.