Eligible for arbitration for the first time, Willemsen was awarded the team's $1.4 million offer rather than his $2.2 million request on Saturday by Gil Vernon, Edna Francis and Steven Wolf, who heard arguments a deal earlier.
The 31-year-old right-hander was 3-2 with a 2.27 ERA last season in 57 relief appearances and made $528,800. He saved 53 games in 63 chances the previous two years but had command problems and lost the closer's job.
Teams won eight of 14 decisions this year, the most cases since they also went 8-6 in 2001, and are 301-221 since arbitration started in 1974. Baltimore beat outfielder Alejandro de Aza, who will get $5 million offer rather than his $5.65 million request.