Tonelli was the first 15-year-old player to be signed by the Toronto Marlies OHA team, and the first Miltonian to play with the Marlies since Murray "Cowboy" Grenke in the 1948–49 and 1949–50 seasons. In his first season with them, Marlies' coach
George Armstrong noted Tonelli was pro material.
Contract dispute between OHA and WHA Tonelli was one of the first players to challenge the Ontario Hockey Association and the Marlies OHA team, with which he had signed a contract at age 16. As he reached age 18, the
WHA's Houston team offered him a contract worth $500,000 ($2.2 million CAD in 2016), but his contract with the Marlies tied him to the OHA team for three years plus an option. In June 1975, the WHA owners voted to void Tonelli's Houston contract. Tonelli's agent threatened to sue, and the Marlies asked for $100,000 in compensation, plus 20 percent of Tonelli's three-year WHA contract. Tonelli refused to play for Toronto in the playoffs after he turned 18, so that it would not imperil his legal arguments. Tonelli's agent Gus Badali sued the Marlies and the OHA, and eventually the Ontario courts ruled that the contract was unenforceable because Tonelli had been under the age of 18 when he signed it, and his parents had not signed it. Tonelli's teammate, future NHLer
John Anderson, followed this same lead, sitting out for a period, but eventually returned to lead Toronto in the
Memorial Cup. Tonelli played for Houston for three seasons. During his time in Houston, he was drafted by the New York Islanders in the second round (33rd overall) in the
1977 NHL Amateur Draft after
Jim Devellano, who was the Islanders Director of Scouting, came and visited Tonelli in Houston. Devellano was the only NHL scout to come and personally visit Tonelli in Houston while Tonelli was there, taking him out to dinner to talk. In his rookie season, the Aeros sought to defend the
Avco World Trophy, which they had won the last two seasons. They reached the Avco Cup Final once again but lost in a sweep to the Winnipeg Jets; Tonelli scored 14 points in 17 postseason games. Up until 1977, Tonelli often suffered once or twice a year from devastating migraine headaches that started age 10 and that doctors said were caused by his intensity and nervousness at game time.
Move to Islanders Tonelli's NHL rights were reclaimed by NY Islanders after the Houston WHA franchise folded in July 1978. In 1982 and 1985, Tonelli was a second team
All-Star left wing for the Islanders. He played in the
Stanley Cup finals in 1980, 1981, 1982, 1983, and 1984 with the Islanders, winning four championships in the process, and made an additional appearance as runner-up in the Cup finals in 1986 with the Flames. On May 24, 1980, Tonelli had the assist on
Bob Nystrom's overtime
Stanley Cup-winning goal against the
Philadelphia Flyers, giving the Islanders their first of four straight Cups. In Game 6 at
Nassau Coliseum,
Lorne Henning stole the puck at center ice, passed to Tonelli, who then criss-crossed with Nystrom, feeding him the puck on Nystrom's backhand for the winning goal at 7:11 of overtime. It was a play the two had perfected during practice. On January 6, 1981, Tonelli scored five goals in a game versus the Toronto Maple Leafs. Tonelli was a gritty forward with a never-say-die attitude for the Islanders. Tonelli, who was affectionately dubbed "The Greasy Jet" by his teammates, is remembered for scoring important "clutch
goals" in the Islanders' run of four straight Stanley Cups and five straight finals appearances, particularly during the 1981-82 season. During the playoffs that year, The Islanders were five minutes away from being eliminated by a much weaker
Pittsburgh Penguin team, trailing 3-1 in the deciding game. Tonelli assisted on a
Mike McEwen goal that closed the champions within one goal, and tied the game himself with 2:21 to play. For an encore, it was John Tonelli that scored in overtime to win the game for the Islanders, thus extending their long reign as Stanley Cup champions. Tonelli also scored the winning goal in a February 20, 1982 game against the
Colorado Rockies, beating former teammate
Chico Resch with just 47 seconds to play to allow the Islanders to set an NHL record (since broken) with their 15th consecutive victory. Early in his Islander days, Tonelli was a curiosity to his teammates. He arrived early and stayed late. He made demands of himself that were so harsh that coaches felt compelled to ask Tonelli to save some of that work for the games. At the time, the
New York Times estimated he was making $200,000 per year on a four-year contract. A book called
Hockey Scouting Report, 1988-89, authored by former NHL goalie
John Davidson, who had played for the Islanders' rival the
New York Rangers — which lost to the Islanders in the playoffs in 1981, 1982 and 1983 — and a couple of other writers, did a report on Tonelli that made his eyes water. "I don't want to point any fingers", Tonelli at the time. "Let's just say that the nature of the game is that some guys out there hold grudges a long time." The book stated about Tonelli: "Once a good skater with a lot of power, Tonelli's skills are now on the downslide. He doesn't have the acceleration he once did, and for a straight-ahead player who had little agility, loss of speed and power is the worst loss that could be suffered. He retains a kind of laziness he's long had, in that he won't backcheck as well as he should, sort of coasting back to save his energy for another offensive rush." Then a free-agent, he said he sensed the Kings were not interested in his returning next season and instead signed with the
Chicago Blackhawks. On February 18, 1992, Tonelli was traded to the
Quebec Nordiques by Chicago for future considerations. He finished the season there before retiring. Tonelli finished his 1028-game NHL career with 325 goals and 511 assists for 836 points. ==Personal life==