Iannetta cleared the bases with a double after Jason Vargas (2-2) intentionally walked Troy Tulowitzki.
Jason Hammel (4-3) got the win by allowing a single run on five hits over 5 1/3 innings. The win gave the Rockies a 13-4 record under interim Manager Jim Tracy, who replaced Clint Hurdle May 29.
Jose Lopez gave Seattle a short-lived 1-0 lead with a sacrifice fly in the first inning.
The Rockies tied the score in the second on a sacrifice by Tulowitzki and then took a one-run lead in the third on an RBI single by Todd Helton.
The Colorado bullpen held the Mariners in check after the fifth-inning uprising. There was a 55-minute delay in the sixth due to a tornado warning in the Denver area.
Copyright 2009 by United Press International.