Derbyshire 170 for 2 (Guest 76*) trail Northamptonshire 422 (Keogh 102, Bartlett 76, Broad 75, Vasconcelos 53) by 252 runs
The wicket-keeper scored an unbeaten 76 to steer the home side to 170 for 2 in reply to Northants 422 all out on the second day of the Division Two game.
Derbyshire had a relatively new ball to work with at the start of play but could not make the early breakthrough they needed on the second morning.
The pattern of the first day was repeated as Blair Tickner and Anuj Dal beat the bat a number of times but Keogh and Broad maintained their concentration to accumulate steadily.
Broad was the first to his personal milestone, completing a half-century from 98 balls before Keogh guided Dal to the third man boundary to reach three figures.
It had come off 215 balls and contained only nine fours but it was a fine example of disciplined batting at a time when his team needed to rebuild.
Derbyshire had gone into the match without a frontline spinner and it was not until skipper David Lloyd decided to give his own off breaks an airing that the breakthrough came. He saw Broad dropped at point on 65 but in the same over, Keogh edged a drive and was caught at slip.
Broad quickly followed, lbw to Zak Chappell as he played around his front pad and after Wayne Madsen bowled his off-spin for the first time since shoulder surgery in 2022 to improve the over rate, Lloyd beat Michael Finan’s attempted drive.
But by then, Derbyshire had conceded 400 runs for the fourth consecutive championship match although it took only three overs after lunch to polish off the tail.
Tickner deservedly picked up a second wicket when Ben Sanderson edged a drive to second slip before Siddharth Kaul was cleaned up by Daryn Pavillon.
Derbyshire were still facing a formidable total and batting for the first time since they were bowled out in 26 overs against Sussex so there might have been some nerves in the home camp when Lloyd went in the third over.
Sanderson found just enough movement to draw Lloyd into a shot but what followed was remarkable as Broad went full length at fourth slip to take an amazing catch inches above the turf.
But Northants were unable to press home their advantage as Luis Reece and Guest displayed good judgement and application to bat through until tea.
The pair looked to be building a significant partnership until Reece swept Laim Patterson-White and picked out Finan at deep square leg.
Reece knew he had given his wicket away but Guest completed his third fifty of the season and with Madsen made sure there were no setbacks by batting through 24 overs to stumps.
Source: ESPN Crickinfo