Given just one run to work with today, Chris Tillman made it stand up, once again beating the team that drafted him in the second round in 2006.
It is the first time in club history that the Orioles won 1-0 on a leadoff home run.
In winning for the seventh time in 10 games and the 20th time in 29 games, the Orioles concluded a 4-2 homestand and improved to 62-48.
The Orioles have won four series in a row for the first time all year.
Tillman gave up just four singles in a dominant performance. He did not walk a batter and fanned six. He retired 16 of the last 17 hitters he faced as he improved to 8-5 with an ERA of 3.78.
In six career starts against the Mariners, Tillman is 6-0 with a 2.03 ERA. He has pitched to an ERA of 2.38 over his past 11 starts. This was his first win since June 27, ending a six-start winless run.
Markakis started the last of the first with a homer over the right-field scoreboard off Hisashi Iwakuma. He hit a 3-2 pitch for his ninth homer of the year and his first-ever leadoff homer.
It was part of a big day for Markakis. His single in the third inning was the 1,500th hit of his career. He is sixth on the O's all-time list and the second outfielder in club history with 1,500 hits. Brady Anderson had 1,589. Markakis went 3-for-4, adding a single and double. He had three of the Orioles' five hits.
Iwakuma (9-6) was a tough-luck loser, allowing just five hits and one run over 7 2/3 innings.
The Orioles scored just six runs in this series, but won two of three. They've scored three runs or less in seven of their last nine games.
This was a rare Sunday home win for the O's, who are now 8-10 on Sundays in 2014 and 3-6 at Camden Yards.
Now the Orioles head to Washington Monday night for a makeup of a rainout against the Nationals. Kevin Gausman (5-3, 3.70 ERA) faces Tanner Roark (11-6, 2.74 ERA) at 7:05 p.m.