The Kansas City Royals are working on what would be the first combined perfect game in baseball history against the Cardinals through seven innings Monday in St. Louis.

Reliever Josh Staumont started the game as the opener and retired the three batters he faced. Mike Mayers relieved him and retired the next 18 in order.

Royals outfielder Drew Waters kept the perfect game going with a diving catch of Tommy Edman's sinking liner into center field to end the sixth inning.

Major League Baseball hasn't seen a perfect game since Aug. 15, 2012, when the Seattle Mariners' Felix Hernandez did not allow a baserunner in a 1-0 win over the Tampa Bay Rays.

The Royals have never been involved in a perfect game on either side. The franchise's last no-hitter was Aug. 26, 1991, when Bert Saberhagen yielded no hits against the Chicago White Sox.