Northants 128 for 5 trail Glamorgan 233 (Lloyd 92, Kleinveldt 5-83, Stone 4-73) by 105 runs
Lloyd made a breezy 92 in the morning session - the first uninterrupted session of the match - and looked set for a maiden first-class century at the age of 23 but fell to a fine diving catch by Richard Gleeson running to his left from deep point.
"It was a very good experience for me," Lloyd said. "It was a tough wicket and to get 92 was a highlight of my career so far. I was disappointed not to get over the line but it wasn't meant to be and hopefully there are plenty more chances to get a hundred.
"I thought the way the wicket was playing and what the ball was doing, I thought maybe the way was to be as positive as I could be, going hard and attacking just paid off in the end so hopefully it's helped the team's cause with a few more runs than we were going to get at one point, and it came off."
Lloyd began the day on 64 not out - already his first-class best score - and continued to play with a freedom not seen throughout the rest of the order in swinging conditions. His driving was especially impressive.
In total Lloyd struck 15 boundaries in his 106-ball stay and gave Glamorgan a batting bonus point and a smart recovery from 84 for 5.
Jones, a 21-year-old from North Wales, then took his chance with the ball to take the first two wickets of his first-class career on debut. He was handed the final over of the morning session and with the last delivery, shaped one away from Ben Duckett to have the left-hander caught behind for 20.
Jones' second-wicket was the Northants captain Alex Wakely, who played confidently for his 40 before edging behind. Rob Keogh followed in the same manner off Graham Wagg, who also removed Josh Cobb, bowled for a 13-ball duck. It left Northants struggling to get on terms with Glamorgan but bad light around 3pm took the players off the field and they did not return.
But there was at least some meaningful cricket in the morning session and Olly Stone took the remaining three wickets in the Glamorgan innings, on the day he was named in the England Performance Programme Squad for the winter training camps in South Africa and Dubai.
Stone began with a sharp delivery that Andrew Salter could only fend off to leg gully. Jones was caught in the cordon before Lloyd's wicket gave Stone 4 for 73 and 38 County Championship wickets for the season.