When the same teams open a three-game series at Angel Stadium on Friday night, the Mariners won't have that comfortable lead.
Seattle has gone 8-10 since July 4 and its advantage over the surging Oakland A's was whittled to 1 1/2 games entering Thursday. The Mariners (61-41) haven't won two straight games since taking eight in a row from June 25 to July 3.
"You go through these stretches through the course of the season and it's tough," Seattle manager Scott Servais told reporters after a 3-2 win over the San Francisco Giants on Wednesday. "It's not like these guys aren't trying."
The Angels (52-52) ended Seattle's winning streak with a 7-4 victory on July 4 in Seattle, but they haven't taken advantage of the Mariners' recent inconsistency.
Oakland has, winning five straight entering Thursday and 14 of 18 since July 3.
The Angels dropped two of three at the Los Angeles Dodgers heading into the All-Star break. They are are 3-4 coming out.
They picked themselves up after losing the first two games of a four-game series against the Chicago White Sox earlier this week by combining for 23 runs in victories on Wednesday and Thursday.
The Angels are 10 games behind the Mariners with the A's and Tampa Bay Rays in between.
"We're going to keep grinding as an offense," Angels left fielder Justin Upton told AM 830 after the 12-8 win on Thursday. "See what we can do. See how many games we can win."
Seattle left-hander Wade LeBlanc and Los Angeles left-hander Andrew Heaney will go head-to-head for the third time since June 11.
LeBlanc (6-1, 3.44) is 2-0 in those games with a 2.25 ERA, his only two appearances against the Angels in his 10-year career.
LeBlanc is the one who extended the winning streak to eight games when he limited the Angels to one run and three hits in seven innings of a 4-1 win on July 3. Heaney also went seven innings, allowing two runs and five hits.
They matched up again on June 11 and LeBlanc gave up two runs and five hits in five innings. Heaney lasted just three innings, his shortest outing of the season, allowing five runs and seven hits in a 5-3 loss.
Heaney is 1-3 with a 3.91 ERA in five career starts against Seattle.
Heaney (6-6, 3.66) has pitched well so far in July, owning a 2-1 record and a 2.73 ERA.
In his most recent outing, Heaney accomplished something few Los Angeles pitchers have done the past few seasons, outdueling a member of the Houston Astros staff. He allowed one run and four hits in six innings on Sunday, and the Angels supported him with four home runs in the 14-3 victory.
"We've got to be able to carry that over moving forward," Heaney told MLB.com after the win. "We've got to do it a lot more often. It's time to get going."