Hernandez, who signed a seven-year $175 million deal last month, struck out two and threw 33 pitches.
Romero, an infielder, finished 4-for-5. He had a grand slam in the fourth inning and a three-run shot in the ninth.
Casper Wells hit a three-run homer in the eighth. The Mariners have 10 consecutive multi-homer games and top the majors with 29 home runs.
Hisashi Iwakuma allowed one hit in three scoreless innings for the victory.
Royals starter Ervin Santana struck out four in three innings and allowed a run and three hits.
More Sports Headlines
An open letter to new M's GM Jerry Dipoto Seahawks' Lynch, Mebane won't play Monday night against Lions 1:25 p.m. Bengals stay unbeaten with 36-21 win over Chiefs 1:58 p.m. Newton, Norman lead unbeaten Panthers to 37-23 win over Bucs 1:57 p.m. Freeman scores 3 TDs as unbeaten Falcons beat Texans 48-21 1:57 p.m. Colts tie NFL record, beat Jaguars 16-13 in overtime 1:57 p.m. Manning throws 3 TD passes as Giants beat Bills 24-10 1:46 p.m. Cutler, Gould lead Bears to 22-20 win over Raiders 1:46 p.m.
Our new comment system is not supported in IE 7. Please upgrade your browser here.