The new government here is racing to carry out an ambitious 100-day plan to overhaul the constitution and reinvigorate the economy as it girds for elections likely within the next few months.
But on Saturday, Prime Minister Ranil Wickremesinghe took a break from affairs of state—to watch a high-school cricket match.

It isn’t just any game. Known as the Battle of the Blues, it has been played annually for 136 years between two of Sri Lanka’s oldest and toniest all-boys schools, Royal College and S. Thomas’ College.
The three-day match is among the most important social events for members of the Colombo elite, who gather in grandstands and tents festooned with bunting to party, schmooze and watch cricket.

“It’s like an annual pilgrimage. You come to meet your old friends,” said Dilshan Jayasuriya, a lawyer who graduated from S. Thomas’ in 1994. Luckily play ends on a Saturday, he said, since “it takes one full day to recover.”

About 30,000 people turned out to watch, according to organizers. Alumni, known as Old Royalists and Old Thomians, flew in from around the world.
This year the celebrations also had political overtones, because the prime minister and a dozen other cabinet ministers and deputy ministers are graduates of Royal College. The new government led by President Maithripala Sirisena took office in January after voters ousted former President Mahinda Rajapaksa, whose main base of support has been in rural areas.

On Saturday morning, Mr. Wickremesinghe turned up in his trademark yellow shirt (Royal’s colors are blue and gold) and stopped in at the Mustang tent, his usual match haunt and one of the most exclusive venues for watching the game.

“He always goes,” said a spokesman. “He considers it his duty as a Royalist.”
Royal College traces its origins to the 1830s in what was then British-ruled Ceylon. S. Thomas’—which uses the initial S. instead of the more common abbreviation St. for saint—was founded by an Anglican bishop more than 160 years ago.

Modeled on British public schools, they have long produced an outsize number of Sri Lanka’s political and business leaders and professionals. Their athletic rivalry is interwoven with national history. The teams vie for the D.S. Senanayake Memorial Shield, named after Sri Lanka’s first post-independence prime minister, who played in the Royal-Thomian cricket match as a S. Thomas’ student at the start of the 20th century.
On Wednesday, the day before the match, students from both schools paraded through Colombo. An elephant strode ahead of a red double-decker bus carrying members of the Royal team, resplendent in their school ties and striped blazers on the open upper deck.

Play started on Thursday. And for many in the capital, serious business ground almost to a halt. Turnover on the Colombo Stock Exchange hit its lowest level in nearly a year on Friday.
“A lot of Royalists and Thomians are employed at the bigger brokering firms,” said Prasanna Chandrasekara, a director at Softlogic Stockbrokers. He put in 90 minutes at the office Thursday before heading to the match and took all of Friday off.

“When you are at the match, it’s like going back in time” to your school days, said Mr. Chandrasekara, who attended S. Thomas’ and hasn’t missed a match in 20 years. “Even when the match stopped for rain today, the partying went on for six more hours.”
Indeed, the downpour that halted play shortly after noon on Saturday did little to dampen spirits. As teenagers in white uniforms and straw hats decorated with cockades in their school colors roughhoused on the muddy grounds, Old Boys sipped drinks and listened to music.

Live bands in some tents, many with equine names such as Thoroughbreds, Broncos and Cavalry, competed with high-decibel dance music pumping out of others. In some, dancers provided entertainment. One had disco lights.
Among the Colombo elite, where you studied matters. “When you meet someone, it’s one of the first questions you ask,” said Harini Amarasuriya, a sociologist at the Open University of Sri Lanka. “It’s not just a sentimental attachment. It can determine your job, who you marry, what clubs you belong to.”
Eran Wickramaratne, an Old Royalist who is now deputy minister for investment and highways, said Sri Lankans make too much of where they went to high school.

Still, he said, playing cricket was transformational for him. He played in Royal-Thomian matches in 1976 and 1977. “Sports taught me discipline,” he said. “Leadership isn’t something you learn from books or in the classroom. You learn it on the field.”
Both schools say they try to transcend the ethnic and religious divisions that have bedeviled their country, accepting students from all communities. And they seek to build character.

“We send men into the world with integrity and courage. That’s our main objective,” said the Rev. Marc Billimoria, the Anglican priest who is warden of S. Thomas.’
At Royal, boarding students are supposed to rise at 5 a.m. and start their day with calisthenics before heading to class at 7. On weekends they can sleep in—until 6.
Sports are a big part of life at both schools, and the Royal-Thomian cricket match is the biggest event of the year.

“There’s a lot of history, a lot of responsibility on our shoulders,” said Thiran Dhanapala, a Royal player. “There are so many distractions, it’s hard to focus. But you have to do it for the school.”
To concentrate on match preparations, the Royal players lived together in a dormitory and tried to isolate themselves from the outside world. That meant no phones and no contact with girlfriends.
“There’s a lot of pressure,” said Harith Samarasinghe, the Royal captain.

After three days of rain-interrupted play, the 2015 match ended in a draw Saturday, with Royal unable to complete its innings because of the weather.
So, as tradition dictates, the D.S. Senanayake shield will go back to Royal College, which won it in 2013. (Last year’s match also ended in a draw.) There it will sit in a trophy case until the next round of the Battle of the Blues.

—Uditha Jayasinghe contributed to this article.

Photo Caption - Ranil Wickremesinghe, prime minister of Sri Lanka, at the Royal-Thomian cricket match. Photo: Junho Kim for The Wall Street Journal

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