Nottinghamshire 285 (Montgomery 80, Hameed 70, James 50, Hogan 4-47, Harris 4-65) and 259 for 4 (Clarke 95, James 76*) drew with Glamorgan 318 and 421 for 5 (Byrom 144, Northeast 105*, Lloyd 60)
Nottinghamshire showed why they are leading the way in Division Two by batting through the day in Cardiff to frustrate a Glamorgan side who needed nine wickets for victory.
Glamorgan were left to rue a couple of decisions which could have exposed the Notts tailenders to the second new ball, but the Cardiff wicket remained true and in the end the pursuit was called off with just over nine overs to go as both sides agreed a draw.
The Welsh County were only able to take three wickets on the final day, two of those to the occasional spin of Colin Ingram and Kiran Carlson, and they were unable to claim the win that would have moved them second in the table.
Notts will feel they have earned their cushion in the promotion hunt, with a 19-point gap to third-placed Worcestershire and Glamorgan a further four points behind that.
Clarke would have enjoyed giving Welsh cricket fans an exhibition of his talents as he will be back at the Cardiff Wales Stadium on a regular basis in the next few weeks as part of the Welsh Fire squad in the Hundred.
He came to the wicket early as Glamorgan got the perfect start, James Harris trapping Matt Montgomery lbw in the second over of the morning. Getting rid of the first-innings top-scorer seemed a crucial breakthrough for the Welsh county.
However they had to wait until six minutes before lunch for another wicket to fall as Clarke and Ben Slater successfully blunted the bowling attack.
Glamorgan captain David Lloyd ran through his options and brought on Ingram, who lured Slater into giving a caught-and-bowled chance with the batter departing for 48.
That put Notts three down at lunch, probably the minimum Glamorgan required to continue their push for victory.
The afternoon session was one of frustration for the bowlers with even half chances few and far between as Lyndon James joined Clarke and the pair took the score to 184 for 3 at tea.
Clarke seemed odds-on to move onto his century, especially when Glamorgan brought on part-time spinner Carlson for the first over after tea.
An innocuous ball outside off stump flicked Clarke’s edge, Chris Cooke took the catch and suddenly the game was thrown open.
Glamorgan took the second new ball as soon as it was available with 25 overs to go and the mood of the game changed as Notts captain Steven Mullaney joined James at the crease.
Australian Michael Neser charged in with the new ball and had a strong lbw shout against Mullaney turned down second ball, while the fifth ball was edged past first slip.
A couple of overs later he had a huge appeal for caught behind, again off Mullaney. The Glamorgan players sank to the ground when umpire Hassan Adnan kept his hand down, knowing a win was slipping away.