Clements continued his career with the Saskatchewan Roughriders in 1979, but did not fare well, throwing only two touchdowns to 11 interceptions and being replaced by Danny Sanders. However, a trade to the Hamilton Tiger-Cats quickly rejuvenated Clements, and he led the CFL in passing yards with 2,803, the last to do so with less than 3,000 yards. In 1980, Clements was briefly on the roster of the NFL's Kansas City Chiefs, coached by former Montreal Alouettes head coach Marv Levy, but was the third-string quarterback for a team that stressed the running game. In 1981, Clements returned to the Tiger-Cats and threw for 4,536 yards. He improved his numbers the next season with 4,706 yards. In 1983, Clements was traded from Hamilton to the Winnipeg Blue Bombers for long-time Blue Bomber quarterback Dieter Brock. The next year, those two teams, Hamilton and Winnipeg, faced each other in the Grey Cup. Clements led the Bombers to their first Grey Cup victory since 1962. In 1986, he set a new completion percentage record with 67.5, 173 out of 256. Clements finished his playing career with Winnipeg in 1987 and was also named the league's Most Outstanding Player. He finished his CFL career with over 39,000 passing yards, 252 passing touchdowns, and a 60.35 completion percentage. In 2005, for the 75th anniversary of the Winnipeg Blue Bombers, Clements was selected one of the Bombers 20 all-time great players. In addition, in November 2006, he was voted one of the CFL's Top 50 players (#47) of the league's modern era by Canadian sports network TSN.