Wearing his black and gold No. 19 sweater, Thornton would position himself on the blue line directly below and in between the retired jerseys of Nos. 15 and 24, representing Milt Schmidt and Terry O'Reilly. When Thornton was asked back then if he stood there as motivation, hoping that one day his number would hang from the rafters, Thornton never answered; he only smiled.
Thornton's been back in Boston as an opponent several times since the trade, and now there's a rivalry between the Bruins and Sharks. Not every former Bruin (see Phil Kessel) gets the warm reception that Thornton receives when he's back in town, and Thornton was welcomed again Saturday night when the Bruins hosted San Jose.
The Sharks defeated the Bruins 4-2 and Thornton contributed with an assist in the victory. It was an entertaining game, one that could have gone either way, but in the end it was San Jose that came away victorious.
In fact, the Sharks have played well in this building the past few seasons and have won four games in a row at TD Garden.
"It seems every time we play here, they're a real talented team, so it's defense first," Thornton said. "And I think when you've got good defensive teams going toe-to-toe, it seems to be a good game. They've got some good offensive players and it just always seems to be one-goal games, and pretty exciting games, too."
The Sharks came close to facing the Bruins in the Stanley Cup finals last spring, which would have been interesting given Thornton's history with Boston. But San Jose lost to the Vancouver Canucks in the Western Conference finals.
It was the second consecutive season the Sharks reached the conference finals. They bowed out to the Chicago Blackhawks in 2010.
But when the Bruins and the Canucks played in the Stanley Cup finals last spring, Thornton's pick was an easy one.
"I was actually cheering for [Boston] in the final," Thornton said. "After losing against Chicago and then Chicago hoisting it up, and it would have been tough seeing Vancouver hoist it. I was cheering for [Boston] and I still have a lot of friends over there, so I was happy for them.
"They haven't had a Cup here in so long, so it was overdue. It's such a good sports town and it was nice to see the Bruins finally win with the Celtics, Pats and the Red Sox winning in the past, so it was good for them to get theirs."
Thornton said he reached out to members of the Bruins' training staff as well as forward and good friend Milan Lucic after Boston won the Cup. Thornton also planned on offering his congrats during Saturday's game.
Thornton was and has remained a fan favorite in Boston, so coming back occasionally is worth it.
"I enjoy it," he said. "I still have quite a few friends here and we usually get to spend the night, so it's nice. I always love coming back. It's a great sports town and I have a lot of fond memories here."
Thornton entered the NHL as an 18-year-old, and on Friday against the Devils in New Jersey the now 31-year-old played the 1,000th game of his career. During a television timeout with 9:57 remaining in the first period Saturday night, the Bruins honored Thornton for his milestone with a video tribute. The 17,565 fans in attendance gave him a standing ovation.
"It's great," Thornton said of the tribute. "Obviously this is where it all started. They gave me a chance and I love coming back to this city. I've still got so many friends and they're still a part of my life."
As far as the milestone, it's something that surprises even him a bit.
"It seems to come pretty quick," he said. "It's kind of like time flies by and as a kid you just want to get that first game in the NHL, and after that you really don't set your sights on a thousand because it feels so far away. It sneaks by quickly and now it's 1,001 tonight."
He played a total of 532 games with the Bruins and he finished Saturday's game with 307 goals, 698 assists for 1,005 points with 936 penalty minutes in his career.
"Hopefully, knock on wood, you can hit that milestone," Lucic said. "Only a few guys have been able to do that and it's not an easy thing to accomplish. Staying healthy in this league is a tough thing to do. It seems like yesterday I was a kid watching a guy like Joe Thornton just start and here he is playing in his 1,000th game. It's something special for him to accomplish and hopefully one day I get to do the same.
"He's definitely a tough player to play against because he's so big and so strong. If you go at him he makes that special saucer pass and finds guys in the open and that's what makes him a great player. He definitely has that ability to score goals as well and he's been doing it for a long time. He's fun to watch when you do get a chance to watch him."
As much as he was a star in Boston, Thornton has been a significant member of the Sharks' organization and has helped San Jose become a perennial winner.
"In a lot of ways Joe's become a father and has become a more mature man," San Jose coach Todd McLellan said. "He still has that happy-go-lucky jumbo quality that's a very good quality in my opinion. He's very committed defensively and very good on the backcheck, penalty-killing and faceoffs. He has all the characteristics of a good leader. It's not just about what's on the paper at the end of the night as far as goals and assists. He's done a tremendous job. It's his team and the players are following him and doing a pretty good job of it."
Budding Bruins superstar Tyler Seguin was the No. 2 overall selection in 2010 by Boston. Like Thornton, the top pick in the '97 draft, there was a lot of hype surrounding Seguin's arrival and the kind of impact he would have.
Thornton played in 55 games during his rookie season (1997-98) under coach Pat Burns. Seguin played 74 regular-season games and 13 playoff games during his freshman season a year ago.
The Bruins are only eight games into the 2011-12 season, but it's already obvious Seguin's been the team's best forward, producing three goals and six assists for nine points. Seguin scored Boston's second goal of the game on Saturday.
Thornton, who has one goal and three assists in six games this season, understands why the 19-year-old is playing with confidence.
"The first year all about learning," Thornton said. "At least my first year, it's kind of different these days because the coaches have to play the young players. The second year you find your groove and you get a little more confident and you know going into training camp you have a spot on the team and you know what the day-to-day things will be, so every year you should get better."
Thornton had an impact before he arrived in Boston, during his time in a Bruins sweater and even after he skated across to the Western Conference.
If the No. 19 hangs from the rafters at the Garden, Thornton's nameplate won't be on the banner. Barring a return to Boston during his career, his name will never appear on the Stanley Cup as a Bruin. He was rooting for the Bruins last spring, but he said he never thought about what it would have been like if he were a part of Boston's long-awaited success.
"No," he said. "It feels so long ago. You're so consumed on what you have to do in San Jose and there's no what-ifs, no."
Joe McDonald covers the Bruins for ESPNBoston.com.