Northants 102 for 6 (Leach 4-34) trail Worcestershire 188 (Carter 3-51, Buck 3-53) by 86 runs
New skipper Joe Leach inspired a Worcestershire fightback as 16 tumbled on the opening day of the Specsavers County Championship match with in-form Northamptonshire at New Road.
New Northants signing, paceman Andy Carter, enjoyed an inspired debut with a deadly three wicket burst including Worcestershire top-scorer Moeen Ali, who made 50 as the home side were bowled out for 188.
It was the ideal start to Northamptonshire's bid to win the opening three Championship matches in a season for the first time in their history.
But Leach, in his first home match at the helm since replacing Daryl Mitchell as captain, produced a deadly new ball spell which yielded four wickets.
It was reminiscent of the form which brought him 65 Championship wickets last summer - the most by any bowler in Division Two.
When bad light intervened with 25 overs remaining, Northants had been reduced to 102 for 6 with only Ben Duckett (45 not out) offering serious resistance.
Former Nottinghamshire and Derbyshire player Carter was signed up after injuries to pace duo Ben Sanderson and Rory Kleinveldt.
The visitors were also without skipper Alex Wakely for family reasons and Josh Cobb led the side in his absence.
Moeen, playing his first Championship match for almost a year, and Daryl Mitchell dug in against the Northants seamers in adding 62 for the second wicket after the early departure of Brett D'Oliveira.
Steven Crook trapped Mitchell lbw for 30 and Tom Fell departed in the same manner to Mohammad Azharullah.
Moeen had greeted Carter's introduction into the attack by planting his first delivery over midwicket for six and the England all-rounder went to his half century off 87 balls.
But then Carter changed the complexion of the game when he returned after lunch for his second spell. Moeen went for a drive and was bowled and four balls later Tom Kohler-Cadmore, still to get off the mark, shouldered arms and suffered the same fate.
It became three wickets in 11 balls for Carter as Ben Cox nicked a ball of extra bounce through to keeper Adam Rossington.
Joe Clarke produced some flowing drives but Nathan Buck ensured Northants polished off the innings in efficient fashion.
He disposed of Ed Barnard, Leach and Josh Tongue in the space of five overs while Clarke's knock ended at 33 when he fell lbw to Crook.
The wickets continued to tumble when Northants launched their reply with Leach settling into a lengthy opening spell which brought him four wickets.
After Rob Newton went lbw in Leach's first over, Duckett decided attack was the best form of defence in an over from Worcestershire overseas player John Hastings which cost 22 runs.
He was aided by Max Holden in a stand of 53 but it was only a brief respite before the bowlers dominance returned.
Holden drove Barnard to point before Leach took centre stage. Rob Keogh edged to second slip and Rossington rashly slashed the next delivery to point.
Richard Levi survived the hat-trick ball and a spilled chance by Josh Tongue off Leach but it did not prove costly.
He went lbw for 24 in Leach's next over and his replacement Barnard disposed of Cobb in the same manner.