Middlesex's dismissal of Gloucestershire all-rounder Mark Hardinges secured the visitors a second bonus point to put them out of Gloucestershire's reach in the table.
The Middlesex seamer Alan Richardson and the spinner Jamie Dalrymple took four wickets apiece as Middlesex limited the hosts to 333 all out at Bristol.
Malinga Bandara top-scored with 70 for the hosts while the captain, Alex Gidman, and the all-rounder Stephen Adshead also made half-centuries in what proved to be a futile innings. Middlesex made 20 without loss before stumps.
Relegated Glamorgan limped to 151 all out at Sophia Gardens as Greg Smith took 4 for 28 for Nottinghamshire.
Smith and the former England seamer Ryan Sidebottom, who took 3 for 31, led the attack as Glamorgan struggled to produce any kind of momentum, with Mike Powell , who hit 62, the only batsman to make more than 22.
Nottinghamshire then raced to 151 for 2 in response with Darren Bicknell unbeaten on 81 and Russell Warren impressing with 51 after Jason Gallian went for a duck, caught by Mark Wallace off David Harrison.
In the Second Division, John Maunders helped Leicestershire to put themselves in a strong position against Worcestershire at Grace Road.
Maunders hit 148 as the Foxes finished the opening day on 342 for 7. However, the left-hander received inadequate support from his colleagues.
Only the Leicestershire wicketkeeper Paul Nixon, who was unbeaten on 37 at the close, came anywhere close to reaching a half-century.
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