With a relatively low total to chase down, Gladiators went past Zalmi courtesy an unbeaten 51-ball 58 from Ahmed Shehzad
Quetta Gladiators hope their in-form opener Shane Watson will make them third time lucky as they look to avoid another knock-out punch
Openers Kamran Akmal (74 off 43) and Imam-ul-Haq (58 off 33) set the platform for a massive target with a 135-run opening stand.
Islamabad will now clash with Peshawar on March 14 and the winner will face-off Quetta Gladiators on March 17.
Islamabad, champions in 2016 and 2018, were equal on points with their rivals in the league phase with 10 in as many games
Quetta Gladiators are through to the PSL 2019 final after they survived a Sammy and Pollard onslaught
Quetta Gladiators and Peshawar Zalmi have squared-off three times in as many seasons in the playoffs with the margin of victory being just one run
Hales, a top-order batsman for England, will be making a comeback to Islamabad United after representing them in four matches during the last season.