Edgars Kulda and Luke Bertolucci each scored twice for the Oil Kings, who played their second game in as many nights and improved to 1-1.
Kulda had an assist for a three-point night and Reid Petryk also scored for the Western Hockey League champions. Oil Kings goaltender Tristan Jarry stopped 38 shots, including a penalty shot late in the first period.
The Knights fell to 0-2. London must win the final round-robin game of the tournament Wednesday against the Ontario Hockey League champion Guelph Storm to avoid elimination.
Oil Kings head coach Derek Laxdal was just glad it won't be his team up against the same wall Tuesday against the Val-d'Or Foreurs.
"To get that first win tonight gives our kids a little bit of confidence with a day of rest and get ready for a huge game Tuesday against Val-d'Or," Laxdal said. "Every game gets bigger now as the tournament moves forward."
The Foreurs are the Quebec Major Junior Hockey League champions and take on the Storm on Monday in a clash of the 1-0 teams.
The Knights were one of three OHL teams to score more than 300 goals during the regular season. The Storm eliminated London from the OHL playoffs April 11 and the Knights offence has sputtered to start the Memorial Cup.
Their first two goals of the tournament Sunday were scored by defencemen Alex Basso and Dakota Mermis. London was scoreless on a seven power-play chances in their first two games. What's more glaring is the Knights were 0-for-2 in penalty shot attempts in the two games.
"We've scored two goals in the past two games," Knights right-winger Michael McCarron. "That's not good enough for us. We have so much power up front that we should be scoring four or five goals a game."
Basso reduced Edmonton's lead to 2-1 at 16:12 of the second period, but Kulda's second of the period less than two minutes later killed London's momentum. The Knights were also hampered by taking eight minor penalties.
The Oil Kings finally scored a power-play goal after starting the tournament 0-for-11. Bertolucci ended that frustration with his second of the game at 18:23 of the third period, when McCarron was in the penalty box for punching Mitch Moroz in the face.
Knights coach Dale Hunter pulled starting goalie Anthony Stolarz after two periods for backup Jake Patterson. Stolarz gave up three goals on 30 shots, while Patterson allowed two on 13.
"Coaches just do it to change the momentum of the game and get the kids re-focused," Hunter said. "It was just trying to get team going."
The Knights opened the tournament with a 1-0 loss to the Foreurs despite outshooting them 51-28. Edmonton fell 5-2 to the Storm on Saturday night.
The team with the best round-robin record gets a bye to Sunday's final. The clubs finishing second and third meet in Friday's semifinal. A tie for third means a tiebreaker game Thursday.
Knights forward Ryan Rupert was hauled down on a breakaway late in the first period by Oil Kings defenceman Ashton Sautner. Jarry squeezed his pads together to foil Rupert's five-hole attempt.
Val-d'Or goalie Antoine Bibeau stopped London's Bo Horvat on a penalty shot in the tournament-opener.
The Windsor Spitfires opened the 2009 Memorial Cup in Rimouski, Que., with a pair of losses and won their last round-robin game, a tiebreaker, the semifinal and the final in a five-day span.
The Knights must run the same table to claim the Cup.
"We've got to win the last game or we're out," Basso said.