The 21-year-old Jamaican scored a goal in each half Sunday as the Whitecaps defeated the Houston Dynamo 3-1 in Major League Soccer play.
Mattocks, the second overall pick in the 2012 MLS Superdraft, missed about six weeks earlier in the season while recovering from severe burns suffered during a cooking accident at home.
He's been back for a month, but had played just 100 minutes entering Sunday's game.
"When you get your chance you just have to make full use of it," said Mattocks, who despite limited action is now tied for the team lead with three goals.
He scored 21 goals in 22 games at the University of Akron last season and scored in the 90th minute of Vancouver's last contest, a 1-1 tie with Portland two weeks ago.
"I know I'm capable of scoring goals," said Mattocks, who made just his second start of the year Sunday. "That never came back into my mind. I just wanted to get back into the playing pitch as fast as possible and do what I was brought here to do."
The speedy Mattocks opened the scoring in the fourth minute against Houston. Young-Pyo Lee rushed down the right side and centred the ball to a streaking Mattocks, who one-timed a volley past Dynamo goalkeeper Tally Hall.
"One thing about him is he creates chances," Vancouver head coach Martin Rennie said. "Today he created maybe four, five or six chances. If he gets consistent with his finish he can score a lot of goals."
Mattocks stretched the Vancouver lead to 2-0 in the 66th minute after taking a feed from Gershon Koffie and firing a right-footed shot past Hall.
The 20-year-old Koffie was another bright spot for Vancouver on Sunday, setting up numerous chances for his teammates.
"Those were fantastic passes," said Mattocks of his chemistry with Koffie. "He knows I'm a player that likes to get behind so playing with Gershon is really great for me."
Added Koffie: "I know (Mattocks) can run fast, so I always tell him, 'You don't have to come for the ball, just keep running.'"
Jordan Harvey had the other goal for Vancouver (6-3-4), which was playing its first game since May 26.
"You look at the stages of the season and we started a new one today," Vancouver captain Jay DeMerit said. "To start off on that note is a major positive."
Houston substitute Macoumba Kandji replied for the Dynamo (4-4-4).
Houston was without Geoff Cameron, Canadian international Andre Hainault, Je-Vaughn Watson and Jermaine Taylor, who are all with their respective national teams and make up much of Houston's backline.
"You look at the advantages you have to take on certain nights," DeMerit said. "I think we did that tonight. They're missing a couple of their key guys. We exposed them well at the back."
After opening the scoring, Mattocks had another great scoring opportunity in the 22nd minute after taking a feed from Sebastian Le Toux but he fired a bouncing ball high over the net.
Houston started to press as the first half wore on as Brian Ching blocked a Joe Cannon goalkick in the 28th minute but failed to capitalize.
Cannon made up for that mistake in the 41st minute with a great save off Bobby Boswell. The Houston defender had lots of time after taking a cross at the top of the box, but Cannon jumped high and to his right to punch the ball out of harm's way.
"It was huge," Rennie said of the save. "He's done that on so many occasions now. It often gets overlooked. Those saves are game-winning saves. That would make it 1-1 and that changes the face of the game."
The Dynamo continued to press early in the second half before the Whitecaps started to take control.
"Houston are a top team in MLS and they put us under a lot of pressure at the end of the first half and the start of the second half," Rennie said. "But one of the signs of improvement is we stood up to that and came through in the end."
Vancouver's Davide Chiumiento had a nifty play just prior to the 60-minute mark but his shot slid just wide of the post.
Hall was forced to bat away a drive off the foot of Koffie in the 71st minute to keep his team's hopes alive at 2-0.
The Dynamo cut the Vancouver lead in half in the 83rd minute when Kandji took a pass from Brian Ownby and fired a shot past Cannon for his first goal with Houston.
But Vancouver put the game out of reach in the 88th minute when Harvey took a pass from Koffie and beat Hall for the defender's first goal since 2010.
The game was the only contest on the MLS schedule. Many players are away from their clubs, currently participating in 2014 World Cup qualifying tournaments.
The Whitecaps were without Omar Salgado, who was injured while playing for the U.S. under-20 team last week. Michael Boxall is currently with New Zealand's national team for qualifying. Vancouver was also without the injured duo of Atiba Harris and backup goalie Brian Sylvestre.
Notes: Cannon made three saves, while Hall finished with four. ... With the win, Vancouver moved past Colorado into fourth place in the Western Conference. ... Houston, which had a four-game undefeated streak snapped, missed a chance to move from seventh to fourth in the Eastern Conference standings. ... Attendance at B.C. Place Stadium was 18,811. ... Vancouver hosts Colorado on Saturday, while Houston welcomes FC Dallas.