Zheldakov scored at 1:30 of overtime to lead Russia to a nail-biting 2-1 win over the Czech Republic in quarter-final action Monday.
"It's the best goal of my career so far," said Zheldakov through an interpreter.
Zheldakov took a pass from Nikita Kucherov and blasted a slap shot past Czech goalie Petr Mrazek.
"I looked at the goalie and decided to shoot on the blocker," Zheldakov said. "I was lucky to score."
After the game, Mrazek was incensed that the play should have been whistled down as Czech defender Daniel Krejci was sprawled face down on the ice after taking an apparent high stick to the face.
"I thought that was a penalty for sure," Mrazek said. "Everybody saw it was high stick on the highlights too and he didn't call."
Russia now advances Tuesday night’s semifinal against Canada at the Scotiabank Saddledome Canada and Russia met in the final of last year's championship in Buffalo, N.Y. Canada led 3-0 after two periods, but Russia stormed back for a 5-3 win.
Danil Apalkov scored in regulation for Russia, while goalie Andrei Vasilevski made 38 saves to record the victory.
Jakub Culek scored in the second period for the Czech Republic, which will play Slovakia in the fifth-place game on Wednesday.
In the other quarter-final, Finland defeated Slovakia 8-5 and will face Sweden in the semifinals.
In relegation-round action, Switzerland edged Denmark 4-3 in overtime.
Mrazek, who plays for the Ontario Hockey League's Ottawa 67’s, stopped 43 of 45 shots he faced in the Czech net and received a standing ovation from the crowd of 16,581 fans.
"That's an unreal thing if you lose and the people still stand up and say our names and stuff," Mrazek said. "It would be much better if we won."
After starting the tournament with three straight wins – 3-0 over Switzerland, 3-1 over Slovakia and 14-0 over Latvia – Russia gave up a three-goal lead and lost 4-3 in overtime to Sweden on Saturday.
Meanwhile, the Czech Republic started off with a 7-0 win over Denmark before losing 5-0 to Canada. The Czechs then stunned the United States with a 5-2 win before suffering a 4-0 loss to Finland in its final preliminary-round game.
The Russians outshot the Czechs 16-5 in the first period but couldn't find a way to beat Mrazek.
Kuznetsov had the best chance to score on a breakaway but he missed a wide open net from close range after making a nice backhand-to-forehand move.
The Czechs battled back early in the second and carried the majority of the play.
"In the first period we didn’t play hard, so we said something in the dressing room," Mrazek said. "In the second period it was much better. In the first 15 minutes they didn't have any chances and we had a couple and we scored just one goal."
Vasilevski made a shoulder save to turn aside a shot by Culek before stopping a shot off the stick of Lukas Sedlak with his blocker.
Persistence paid off for the Czechs at 7:16 of the middle frame when Culek tapped in a great cross-crease feed from Tomas Hertl.
Daniel Krejci nearly put the Czechs up by two goals when he deked his way from the slot to the front of the net before Vasilevski stuck out his left pad to turn aside his backhand shot.
Russia then tied up the game at 1-1 when Apalkov fired a long-range snap shot past Mrazek.
Late in the second period, Apalkov and Yaroslav Kosov broke into the Czech zone on a two-on-one. From his left wing, Apalkov passed over to Kosov, who fired a quick shot on net that Mrazek stopped with his left pad.
After making the highlight-reel save, Mrazek got back up on his skates and lifted up his glove hand in celebration to the delight of the fans.
Mrazek received some help from Vojtech Mozik early in the third period when the Czech defenceman alertly cleared a loose puck in the crease out of harm’s way before any Russian forwards could get to it.
At the 12 minute mark of the third, Mrazek made a great glove grab on a shot from the slot off the stick of Kosov.
Then, with two minutes left in regulation, Mrazek stopped a heavy wrist shot from the slot by Kosov. Not to be outdone, Vasilevski made a nice glove save to thwart a scoring attempt by Czech forward Tomas Filippi.
With 46.8 seconds left in the third, the Czechs were awarded a power play when Kucherov was sent to the penalty box for high sticking. After the Czechs failed to capitalize, Kucherov made them pay by setting up Zheldakov for the game-winning goal in overtime.
"It's unbelievable emotion because we played three-on-four before the goal," Apalkov said. "I was so happy."
Finland 8 Slovakia 5
Mikael and Markus Granlund used their offensive skills to lead Finland out of the quarter-finals at the IIHF world junior hockey championship.
If they hope to beat Sweden in the semifinals, the brothers agreed the Finns have to play better in both zones.
"We need to play better defensively," said Mikael Granlund, who had a goal and three assists in the win over Slovakia. "Five goals is too much."
Markus Granlund, who scored twice and had an assist, echoed his older brother.
"Sweden has a very good team," said the 18-year-old forward, a second-round pick of the Calgary Flames in the 2011 NHL draft. "I think we have (to play) defence better and play harder and skate more."
If he and his teammates can shore up some of their problems on defence, Mikael Granlund predicted that the Finns have what it takes to beat Sweden and advance to Thursday's final.
"We'll try to play as good as we can and we have a chance," said the first round pick of the Minnesota Wild. "It's a big rivalry. It's going to be a great game. We have a chance to go to the final, so it’s fun."
Teemu Pulkkinen had a goal and an assist for Finland, while Joel Armia, Roope Hamalainen, Alexsander Barkov and Joonas Donskoi also scored.
Barkov, aged 16 years four months, is the youngest player ever to score in tournament history, beating Canada's Sidney Crosby by 21 days.
Richard Mraz had a goal and two assists while Matus Chovan and Marko Dano each had a goal and an assist for Slovakia. Marek Tverdon and Martin Daloga also scored.
Slovakian coach Ernest Bokros said he's proud his team qualified for the medal round.
"The Slovak team reached the goals that they set before the tournament," Bokros said through an interpreter. "Basically (playing) for fifth and sixth place is kind of like a medal for Slovakia."
Sami Aittokallio made 24 saves for Finland, while Juraj Simboch stopped 30 shots for Slovakia.
Switzerland 4 Denmark 3
Tanner Richard scored in overtime as Switzerland ensured it won't be relegated from the world junior championship.
Cedric Schneuwly, Alessio Bertaggia and Gregory Hofmann also scored.
Vancouver Canucks prospect Nicklas Jensen had two goals for Denmark, which earned its first point of the tournament. Oliver Bjorkstrand also scored.