The left-hander scored an impressive 144 runs off 176 balls to consolidate the Pakistani innings after winning the toss. Pakistan were 352 for four after 90 overs.
The absence of all-rounder Maurice Odumbe in the match meant that the Kenyan bowlers struggled against a strong Pakistan outfit, which included some of the country's Test players.
Odumbe said he was not in the right state of mind to play the opening game after attending a drawn-out inquiry into allegations that he received payments from an Indian bookmaker in 2002.
Skipper Steve Tikolo was forced to bowl all day and his efforts were rewarded when he removed Umar leg before and Pakistani captain Misbah-ul-Haq for 22.
Faisal Iqbal, who partnered Umar in a sparkling fourth-wicket partnership of 161 runs, was 90 not out, while Naveed Latif was on 32 at the end of the first day.