|Ireland 174-4 (20 overs): O'Brien 47, Stirling 39; Masakadza 2-22|
|Zimbabwe: 110-9 (20 overs): Ervine 28, Jongwe 24; Adair 4-23|
|Ireland won by 64 runs and win series|
Ireland move into an unassailable 3-1 series lead after defeating Zimbabwe in the fourth Twenty20 match between the sides at Bready.
Kevin O'Brien led Ireland's batting charge with 47 as Paul Stirling and captain Andrew Balbirnie hit 39 and 37 respectively to leave the hosts on 174.
Mark Adair took a T20 career-best 4-23 with the ball as Zimbabwe fell 64 runs short in their chase.
The fifth and final ODI takes place on Saturday at Bready.
After hitting a superb century on Wednesday, the in-form Stirling moved past England's Eoin Morgan and into sixth place in the all-time T20 run standings with 2,635 runs, with India's Virat Kohli leading the table on 3,159.
Stirling and fellow opener O'Brien done the damage at the County Londonderry venue and their combined total of 86 got Ireland off to a strong start before the pair were dismissed.
O'Brien fell to at the start of the 10th over while Stirling was dismissed three overs later by Wellington Masakadza, however skipper Balbirnie carried on the openers' momentum with a strong 34 alongside Shane Getkate.
William McClintock and George Dockrell took Ireland to the end of their innings and the hosts finished on 174.
After impressing in Wednesday's victory over Zimbabwe with 3-11, Adair again starred and his four-wicket haul marked a career-best performance in the T20 format.
The 25-year-old struck with his first ball as opener Tadiwanashe Marumani was dismissed on four, and he took the wickets of Regis Chakabva and Dion Meyers in the following two overs.
Opener Wesley Madhevere was caught by Shane Getkate as Zimbabwe were left for 30-4 after just five overs.
Ireland's smart work with the ball continued and the tourists were limited to 72-7 when Adair caught captain Craig Ervine on 28 from Simi Singh's delivery.
Adair claimed his fourth wicket to dismiss Blessing Muzarabani on two, and Zimbabwe fell well short of the required total and ended their innings on 110, 64 runs shy of Ireland's total.
The sides complete the T20 series with games at Bready on Saturday before the one-day series starts at Stormont next Wednesday.
T20I series remaining games:
4 September: Ireland v Zimbabwe - 5th T20I (Bready, 15:00 BST)
World Cup Super League series:
8 September: Ireland v Zimbabwe - 1st ODI (Stormont, start 10.30 BST)
10 September: Ireland v Zimbabwe - 2nd ODI (Stormont, 10.30 BST)
13 September: Ireland v Zimbabwe - 3rd ODI (Stormont, 10.30 BST)