They first crossed paths in the early 1990s, adversaries for rival Malaysia Cup sides challenging for silverware. They lifted trophies as players, represented their countries at major tournaments and spent years working their way up the coaching food chain until arriving at the top.
Two decades on from those on-field battles, V. Sundramoorthy and Ong Kim Swee are middle-aged men with greying hair but the competitive fire remains as bright.
Tonight's Causeway Challenge may be an international football friendly, though games between Singapore and Malaysia are rarely boring encounters. But for Sundram and Ong, it is an important chapter in their managerial careers - it is the first time since 1999 that both national teams are helmed by a local - as they seek to lift the gloom that has engulfed their respective teams.
Singapore are 155th in the world and Malaysia three spots below. Neither country has had much to cheer since they last met at the 2014 Asean Football Federation (AFF) Suzuki Cup.
Defending champions Singapore were embarrassed in front of their home fans in a 1-3 loss to the Tigers and eliminated at the group stage. The Lions held Japan to a credible goal-less away draw last year but have been largely uninspiring in the past 22 months.
Causeway Challenge ticket prices
ADULTS: Category 1 - $28, Category 2 - $18.
CONCESSION*: Category 1 - $16, Category 2 - $8
* Students aged 16 and below and senior citizens aged 60 and above.
Tickets are available from sportshubtix.sg, at Singpaore Sports Hub box offices and all SingPost outlets.
Results in Malaysia have been even more dire. There were three 6-0 defeats (by Oman and twice by Palestine) and a 10-0 hammering by the United Arab Emirates last year while a row with Johor Darul Takzim has led to the loss of several key players, including former national captain Safiq Rahim.
A win tonight at the National Stadium will do wonders for morale ahead of the Nov 19-Dec 17 AFF Cup, said Sundram, who turned 51 yesterday and was surprised with a birthday cake after the press conference. He added: "The AFF Cup is our target but in every game we need to play our best and instill winning mentality in the boys. That's good for the long run."
As players, he and Ong, 45, were opposites. Sundram, a Liverpool fan, was flair and skill mixed into an intoxicating blend while Ong, an Arsenal supporter, was the versatile workhorse capable of scoring the odd spectacular goal.
As coaches, they appear cut from the same cloth. Both praised the other's tactical acumen which has seen them lead unfancied but well-organised sides to championships.
The defining moment in their rivalry as players belongs to the Singaporean. Sundram was instrumental in helping Singapore beat Ong's Sarawak in the 1993 Malaysia Cup semi-finals.
"I scored the winning goal," he chuckled.
But it is Ong who holds the edge from the sidelines. He prevailed in their only meeting as coaches (Malaysia's Under-23 edged their U-23 counterparts 1-0 at the 2013 Merdeka Tournament) and was looking forward to pitting his wits against his old rival.
He said: "I know Sundram very well. He likes to make tactical changes in certain games... Singapore are at home and I expect them to press us very early in the game."
The Malacca native is still experimenting with his Tigers - five of his 25-man squad are uncapped - but Sundram dismissed suggestions a full-strength Singapore will start as favourites.
He said: "I expect a tight game. They have young, speedy players on the flanks and I'm sure the new players want to prove themselves to Kim Swee."
This will be the 63rd meeting between Singapore and Malaysia since 1965. Singapore have won 19, three fewer than the visitors.
While that 1-3 loss from two years ago still rankles, it was also a blessing in disguise, said Lions captain Hariss Harun.
"We were a bit naive, a bit inexperienced to handle the match in the closing stages. It was disappointing but maybe also a good thing for the team to learn something," he said.
"We are better prepared now with a couple of senior heads in the team and we hope to handle the match better tomorrow and hope for a positive result."
SINGAPORE V MALAYSIA
Singtel TV Ch109, 8pm