That typical five-day format knock guided Pakistan to a 62-run lead over Sri Lanka's first-innings total of 197.
Umar had provided Pakistan a solid start of 118 with fellow opener Mohammad Hafeez who made an attractive 75.
Despite scoring his second hundred on a comeback trail, his first against the West Indies in May this year, Umar said a comeback was always harder than the start.
"When you do a comeback, you have more pressure on you than your debut," said Umar, who hit eight boundaries during his 296-ball knock. "A century always gives you confidence and I am happy at that."Regarded as Pakistan's best opener when he hit a hundred in his first Test, against Bangladesh in 2001, Umar further gained reputation with a solid 135 against a formidable South African attack at Cape Town in 2002.
But somehow he lost his way.
A ban on former Test captain and opener Salman Butt in spot-fixing, gave Umar another chance and he grabbed it with both hands last year.
"I am more focused now and with the help of coaches Waqar Younis and Mohsin Khan and captain Misbah-ul Haq I have performed well and hopefully carry on the good work," said Umar.
Umar said Pakistan needed the batsmen in the middle.
"We had to spend time at the wicket and the key was the partnerships which you need in Tests. Hafeez and me first with a 100 plus partnership and then with Azhar another, we are in the driving seat right now through that.
"We keep going like this tomorrow as well."
With his sixth Test hundred, Umar has also become the best among his generation, which followed the successful opening pair of Aamir Sohail and Saeed Anwar.
"It is satisfying to be one of the best. I want to perform in every match and try to convert 50s to 100, and I’ve been successful with that as well. I have always wanted to play to what the team’s requirements are," said Umar.