The Portland Timbers had just beaten FC Dallas 2-0 and Vancouver — which was tied 0-0 with the Colorado Rapids after 45 minutes — needed a win of its own to clinch a Major League Soccer playoff spot.
Robinson had banned cell phones in the locker-room to keep his players focused ahead of the match, but was aware of the other score and wanted to make sure his team knew what was on the line.
"I had a decision to let them know at halftime or not," said the Welshman. "I've protected them throughout the season but I wanted them to know what we needed to do.
"I said 'Boys we need to score a goal.'"
After some tense moments, the Whitecaps responded.
Kendall Waston thumped home a header in the 70th minute as Vancouver clinched a post-season berth with a 1-0 victory over Colorado.
The hulking defender flung himself at a Pedro Morales corner kick for a goal his team desperately craved, sending the crowd of 21,000 at B.C. Place Stadium into a frenzy.
"It's a fantastic achievement for the group of players I've got in there," said Robinson. "I couldn't be more proud of them today because we've probably been written off a few times this year when things didn't go our way. In the three years I've been here I've never experienced the atmosphere I experienced today."
Waston only joined the Whitecaps this summer and has been a tower in defence and on set pieces since arriving from a club in his native Costa Rica.
"I was thanking God because it was a nice opportunity to score," said Waston. "We were working very hard from the beginning of the game. We knew we had to win today because Portland won and the only chance we had was winning.
"That was a big effort from all of my teammates."
The Whitecaps finished one point up on Portland for the fifth and final spot in the Western Conference and will now visit Dallas in the No. 4 versus No. 5 one-game playoff on Wednesday.
Vancouver (12-8-14) finished the schedule with four wins and a draw — including four straight shutouts — to make the post-season for the second time in its MLS existence after first qualifying back in 2012.
"I'm ecstatic that we got the win and are in the playoffs. I think we deserved it," said goalkeeper David Ousted after picking up his MLS-leading 13th clean sheet of the year. "These last five, six games people reacted fantastically and we showed we can play against the best and play some good football.
"We're a hard team to score against. Now we need to score a couple more goals and it will all come together, but being hard to score against is important going into a tough playoff and we're happy to move on."
Robinson looked to spark his team early in that second half by bringing on speedy striker Kekuta Manneh, and the 19-year-old caused an immediate buzz, rattling the crossbar in the 58th minute behind Clint Irwin with a shot that beat the Colorado goalkeeper cleanly but stayed out.
A lack of offence — Vancouver went the equivalent of five games without scoring at one point this year — has been a storyline all season and looked like it might sink the Whitecaps until Robinson rolled the dice again by bringing on Erik Hurtado in the 67th minute with his final substitution.
The striker was too sick to start the game, but was right next to Waston when he scored his goal, and nearly buried a chance of his own five minutes later.
Colorado (8-18-8), which was only playing for pride and saw its winless streak hit 14 games, gave Vancouver a couple of late scares, including two efforts from Gabriel Torres that Ousted did well to get behind.
"I think it was fitting David Ousted kept us in with two fantastic saves in the last three or four minutes," said Robinson. "God knows what I would have done if one of them would have gone in."
Added the Vancouver 'keeper: "I kind of had the sense that Portland was going to go there and make it hard for us, and they did. Credit to them. We knew what we had to do in the second half. We did a professional job and got the win."
Despite the joy at the final whistle, it looked early like it might not be Vancouver's night.
The Whitecaps seemed uncomfortable right from the opening whistle, with a number passes and chances going astray.
Waston directed a header wide off a free kick in the ninth minute before Morales, Darren Mattocks and Sebastian Fernandez all missed opportunities of their own later in the half.
"Today's game was the story of our season in 90 minutes," said Robinson. "We played well at times, we had a few half chances (and) we didn't take them. We started to get edgy a bit.
"Part of me believed we might not score if I'm being totally truthful ... but we stuck to our beliefs. The boys kept going. It's a credit to the organization, the supporters, and to that group of players."
The Whitecaps don't have long to celebrate, with a practice scheduled for Sunday ahead of the midweek playoff game in Texas.
"I think we have a chance to go there and win," said Ousted. "They're a good team and they've shown that. That's why they're in the playoffs, but we need to go and see if we can find our style of play there and grind out a win."
Note: The Whitecaps honoured former captain Jay DeMerit before the game. The 34-year-old retired in July and is now an ambassador with the club. ... Both teams had to substitute defenders in the first half, with Steven Beitashour limping off for Vancouver in the 33rd minute, while Marvell Wynne exited for Colorado in the 42nd. Canadian defender Sam Adekugbe was pressed into action for the Whitecaps as a result of Beitashour's injury, with the 19-year-old from Calgary making just the fifth MLS appearance of his young career.
Follow @JClipperton_CP on Twitter