Worcestershire 188 (Moeen 50) and 153 (Buck 4-42) beat Northamptonshire 157 (Leach 5-60) and 164 (Leach 5-62, Tongue 4-45) by 20 runs
Worcestershire made it two wins in a row in the Specsavers County Championship and ended Northamptonshire's 100% start to the season with a victory in two days in a tense, low-scoring contest at New Road.
Having survived a tricky start at 45 for 3, the visitors seemed to be inching towards a third consecutive victory when Adam Rossington and Max Holden played responsibly in a stand of 40.
But the game tilted back towards Worcestershire with two wickets in 13 balls for Leach. The newly-appointed captain had Rossington caught at cover for 22 and then bowled on-loan Middlesex left hander Holden for 37.
Worse followed for Northants when Tongue picked up two in four balls. Richard Levi was lbw for 22, playing back to the 19-year-old paceman, who followed that by yorking Steven Crook.
The two seamers chipped out two more wickets but Mohammad Azharullah kept up the fight with an unbeaten 17 until the result was settled at 7.20pm when Andy Carter was lbw for 8, giving Leach match figures of 10 for 122.
After 16 wickets had crashed under heavy cloud cover on the first day, it was tempting to assume that batting would become easier in bright sunshine, but it proved to be just as difficult to put partnerships together.
In all, 24 fell on a protracted second day.
A grassy pitch, probably typical of early season with its seam movement, was a factor which became critical when coupled with a number of rash shots. Patience was not the name of the game.
The first job of the day was to deal with Northamptonshire's last four wickets and they were duly swept aside in under an hour, although they would have been reasonably happy with the 55 runs added.
Nathan Buck's unbeaten 24 included a pick-up for six off Leach and Crook gave John Hastings the first success in his spell of 3 for 27. With Worcestershire holding a lead of 31, their marginal advantage was quickly diluted with the scoreboard showing 3 for 3 after four overs from Buck and Azharullah.
Daryl Mitchell nicked Buck's third delivery behind the wicket, Moeen Ali scythed a catch to Ben Duckett in the slips and Brett D'Oliviera was given out lbw for a second wicket for Azharullah.
Worcestershire came up with an innovative response by sending in Hastings and Leach in a fourth-wicket partnership after batting at Nos 9 and 10 in the first innings.
The move worked to the extent of 22 for Hastings and 16 for Leach, but half the side went for 56 before regular middle-order batsmen were together at the crease.
Joe Clarke did not last long before edging Buck for another slip catch by Duckett, but hopes were raised by Tom Fell (23) and Tom Kohler-Cadmore (22).
Again, however, it was not as substantial as they would have wanted. Fell was bowled by Buck and Kohler-Cadmore sliced to gully in a short spell by Crook.
Carter, having come out of retirement to sign for injury-hit Northants, took his fifth wicket of the match when Ben Cox was caught behind but the last pair put together the biggest stand of 45 until Tongue was bowled by Buck. Ed Barnard was left unbeaten with top score of 26.