KANSAS CITY, Mo. — When he was traded to the Kansas City Chiefs last offseason, quarterback Alex Smith professed his admiration for coach Andy Reid and his excitement at playing for the storied franchise.

Now, he could have that opportunity for at least four more years.

Smith and the Chiefs agreed Sunday on a $68 million extension that should keep him in Kansas City through the 2018 season, a person familiar with the contract told the Associated Press. The person spoke on condition of anonymity because the deal had not been announced.

Smith, who is due to make $7.5 million this season, will receive $45 million in guarantees.

Smith and his representatives had been discussing an extension for several months, and both sides were hopeful that a deal would be reached by the regular season. But with the Chiefs opening against Tennessee next weekend, time was quickly running out.

The Kansas City Star first reported that an agreement had been reached.

Smith joins a wave of quarterbacks who have recently signed long-term extensions, including the Bengals’ Andy Dalton and Colin Kaepernick, who replaced Smith in San Francisco.

Smith has not played well in the preseason, throwing two interceptions in the red zone in his final outing against Minnesota. But he’s been hampered by an offensive line in turmoil, an injury to running back Jamaal Charles that kept him out two weeks, and a suspect wide receiver group that will start the season without suspended star Dwayne Bowe.

The deal is important for the Chiefs on other fronts, too.

Now that Smith is under contract, they can turn their attention toward a long-term deal with Pro Bowl pass rusher Justin Houston. And if they fail to reach an agreement, the Chiefs could put the franchise tag on Houston without worrying about losing Smith to free agency.

After arriving in Kansas City for a pair of second-round draft picks, Smith had possibly the best season of his career. He threw for a career-high 3,313 yards and 23 touchdowns with only seven interceptions, even while skipping a meaningless regular-season finale.

More importantly, he took a downtrodden team that had won two games before his arrival to an 11-5 record and the playoffs. His won-loss record the past three seasons is 30-9-1 as a starter, trailing only Tom Brady, Aaron Rodgers and Drew Brees in victories among QBs with 30 starts.