Samit Patel, Rumman Raees and Cameroon Delport took one wicket each. Gladiators remained dominated in their chase throughout their batting innings.
37-year old Watson looked in complete control from the very first minute on the pitch till leaving the field after scoring 81 off 55 balls.
Umar Akmal's persistent form in back-to-back matches must have given a thought to ponder over to the selectors months before the coming World Cup.
Meanwhile, Ahmad Shehzad after a golden duck against Peshawar Zalmi, managed to score only two runs. His depleted performance must be a source of concern for the Sarfraz-led team.Sohail Tanvir starred for Quetta in the first innings after picking up four wickets including the all-important wicket of Luke Ronchi who went back to the pavilion after being caught first ball. Tanvir next sent Shadab Khan packing after taking a sharp catch off his own bowling.
This was followed by Mohammad Nawaz trapping Rizwan Hussain for three, leaving United reeling at eight-3 at the end of five overs.
Fawad Ahmed added to United's misery by taking the wicket of Cameron Delport (19) who was caught brilliantly by Tanvir, Hussain Talat (30) and Faheem Ashraf (1) to leave United six down.
Just as Asif Ali stabilised the innings for United, he was caught in the deep end by Nawaz for 36.
Wayne Parnell's blistering 41 of 20 came to an end after helping Islamabad to reach a competitive total of 157.