The pair both represented the United States at the FIFA World Cup in Brazil - Besler in particular being linked with a move to England as a result of his performances.
Fulham and Sunderland were both credited with an interest in signing Besler while Zusi's stock has rarely been higher.
Defender Besler has spent his entire career with Kansas and, like Zusi, has been with the franchise since 2009, helping the club to the MLS Cup last season.
Besler said he was thrilled to stay in the US.
"This is a dream come to true to know that I'll be playing my whole career in Kansas City," he said.
"A lot of factors went into this decision, but the ownership and the great fans played a huge part. Now, there is a responsibility to go forward to keep pushing this team farther and farther."
The pair join Claudio Bieler in becoming a Desgnated Player for Sporting KC and Zusi spoke of his pleasure at being able to see out his career at Sporting Park.
"This is where I have always wanted to be," he added.
"I would like to thank [manager] Peter Vermes and the Sporting Club ownership for working with me toward this long-term contract and I look forward to continuing my career in the best stadium and in front of the best fans in MLS.
"I have always respected players who have played their entire career with one team and I look forward to a long career in Kansas City."
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