It felt like Game 8 of the Western Conference First Round, not the final game of the preseason. The stands were full when the Vegas Golden Knights defeated the San Jose Sharks 5-1 at T-Mobile Arena on Sunday. The penalty boxes were full at times, too.

Seriously? Eighteen thousand one hundred one fans? One hundred fourteen penalty minutes? In the preseason?

That's San Jose-Vegas for you. Suddenly, in two years, after each team eliminated the other in the Stanley Cup Playoffs, it's arguably the best rivalry in the NHL.

"It's one of my favorite games because every time it's like playoff night," Sharks forward Tomas Hertl said. "Like, it's finals. Even if it's preseason or the (regular) season, it's just so much energy."

Just wait. The Sharks and the Golden Knights open their regular season at T-Mobile Arena on Wednesday (10:30 p.m. ET; NBCSN, TVAS), then play again at SAP Center in San Jose on Friday.

"Obviously, there's a lot of bad blood there," Golden Knights forward Jonathan Marchessault said. "It's going to be fun to start. It's a little convenient for the NHL that they put two games back to back for us. Not ideal, necessarily, for us. No, it's going to be good.

"Great rivalry. They have a great team, we have a good team and we'll be good for a lot of years and them also. It's just starting, I think."

The roots of the rivalry trace to the 2018 Western Conference Second Round.

The Sharks had been Stanley Cup contenders for years but made the Stanley Cup Final once, in 2016. In other words, they had paid their dues but were still trying to win the big one.

Video: Golden Knights ride balanced offense to 5-1 win

And along came this expansion team. The Golden Knights went 3-0-1 against the Sharks in the regular season and defeated them in six games in the second round, shutting them out 3-0 to eliminate them on their ice.

Not only that, the Golden Knights won the Pacific Division and went on to the Final.

"I think it started when we lost to them in the playoffs, because they kind of come from nowhere," Hertl said. "First year, and they're doing so good.

"And for sure last year, explode."

Last season, the season series was more even. The Sharks went 2-2-0, the Golden Knights 2-1-1. It was more physical and verbal.

"It just got …" Marchessault said, his voice trailing off. "It just got so intense with them."

Hertl said how the Sharks fared against the Golden Knights would affect them for days.

"I love these rivalry games because you feel like it's so important game," Hertl said. "If you win it, you feel great, so you just keep rolling. If you lose, it's kind of … it's a team we have to beat if you want to go far in the playoff, because we know we will see that team."

The rematch came in the first round.

The Golden Knights took a 3-1 series lead with a 5-0 win in Game 4. It looked like it was over. But the Sharks won 5-2 in Game 5 and 2-1 in double overtime in Game 6 to force a Game 7 in San Jose.

Video: SJS@VGK: Carrier takes lead on tip-in down low

The Golden Knights took a 3-0 lead in Game 7. It looked like it was over yet again. But the Sharks scored four power-play goals during a major penalty in the third period to take a 4-3 lead.

Marchessault tied it 4-4 with 47 seconds left in the third.

"That's the team we are," Marchessault said. "No one gives up in that locker room. That's probably one of the things I'm most proud of. It was one of the best feelings, honestly, to tie it up and bring it to OT.

"We felt in the overtime that we would win that game."

But they didn't.

It was Barclay Goodrow, a fourth-line center, who scored in overtime to give the Sharks a 5-4 victory.

"A couple days after, [president of hockey operations George McPhee is] like, 'You've got to move on' and stuff like that," Marchessault said. "But you don't forget necessarily that easy. So it lingers, obviously. But it's just going to fuel me for motivation for this year, I think.

"We're not mad at them. It's all in their honor. They were down 3-1 in the series. They came back. They scored four goals on the power play. It's all in their honor. I think they took advantage of a situation, and it's not their fault. Good for them.

"At the end, I'm still a fan as a hockey person to watch San Jose. I think they're a fun team to watch."

Well, here we go again.

"It will be great game to start season," Hertl said. "We know the atmosphere there will be insane, same for our building, because it's kind of now 1-1. They beat us first year. We beat them second year in playoffs. So we want to prove it. It will be always, like, 'Who will be better now?'"