Former Mariner manager Bob Melvin has the Athletics in the thick of the AL Wild Card race. The Mariners and Oakland begin a three-game series Monday night. / Wiki Commons

GAME: Mariners (57-66, 3rd, AL West, -13.5 GB) at Athletics (70-53, 2nd, AL West, -0.5 GB). GAME #: 124. SERIES: 1st of 3 games. MEETING: 14th (Mariners lead 8-5). WHEN: Monday, 7:05 p.m., O.Com Coliseum. STREAKS: Mariners W 1; Athletics W 1. TV: Root Sports. RADIO: ESPN 710, Mariners Radio Network

If recent form is any indication, Aaron Harang, scheduled to make his 21st start for Seattle Monday night in Oakland, won’t last very long. He’s gone past 5.0 innings only once in his last six starts. The bad news for Mariners fans there acting manager Robby Thompson will probably have to tap his bullpen early.

Despite Danny Farquhar’s recent run of success — seven saves in eight outings, including a perfect ninth Sunday in a 4-3 win at Texas  — Seattle’s is not a good bullpen. In fact, quite the opposite. With a 4.64 ERA, including a 5.77 mark in August, it ranks 14th in the American League, ahead of only Houston’s (5.24).

You have to go back to Bobby Ayala’s reign of error to find worse Seattle pens than this one. In June, 1999, the Mariners’ bullpen had an 8.48 ERA. The next month, that pen posted a 6.28.

Since then, the highest monthly ERAs by a Seattle bullpen are: 6.98, July 2004; 5.77, August 2013; 5.76, June 2010; and 5.38, July 2009. The main culprit: Oliver Perez. In six appearances, he has allowed eight earned runs in 3.2 innings with an ERA of 19.64. Nine of the last 10 batters he faced reached.

Harang will not face a formidable opponent Monday night. RHP Jarrod Parker is 2-2, 5.10 ERA in five career starts against the Mariners. A closer look:

MONDAY’S PROBABLES

MARINERS: RHP Aaron Harang (5-10, 5.77 ERA, 1.33 WHIP)

The 35-year-old Harang, a San Diego native in his 12th major league season and first with Seattle, will make his 21st start and second against the Athletics. The 35-year-old allowed three runs in five-plus innings against the Rays in a no-decision Wednesday, running out of steam in the sixth when his forearm tightened up. Harang has gone past five innings only once in his last six starts.

• LAST START: Aug. 14 at Tampa Bay, took a no-decision in Seattle’s 5-4 loss; 3 earned runs on 7 hits in 5.0 innings; 5 strikeouts, 2 walks, 1 home run, 103 pitches, 66 for strikes.

• LAST VS. ATHLETICS: June 22, took a no-decision in Seattle’s 7-5 win; 3 earned runs on 6 hits in 5.0 innings; 3 strikeouts, 2 walks, 0 home runs, 95 pitches, 60 for strikes.

• CAREER VS. ATHLETICS: 0-1, 6.23 ERA in 2 starts covering 8.2 innings; 9  strikeouts, 10 walks, 0 home runs, 2.19 WHIP.

• AT O.COM COLISEUM: 3-6, 3.86 ERA in 13 games, including 12 starts, covering 63.0 innings; 47 strikeouts, 31 walks, 3 home runs, 1.66 WHIP.

• LOVES TO FACE: Josh Reddick (0-for-4, .000), Yoenis Cespedes (0-for-3, .000), Seth Smith (2-for-12, .167).

• HATES TO FACE: Eric Sogard (2-for-2, 1.000), Alberto Callaspo (4-for-7, .571), Brandon Moss (3-for-9, .333).

• CURRENT ATHLETICS VS. HARANG: 25-for-80, .33 BA, 11 strikeouts, 14 walks, 5 home run, .411 on-base percentage.

RANGERS: RHP Jarrod Parker (8-6, 3.87, 1.22 WHIP)

The 24-year-old Parker, a Fort Wayne, IN., native in his third major league season and second with Oakland, will make his 25th start and fourth against the Mariners. Parker yielded one run in a career-high 8.1 innings in his last outing, a no-decision against the Astros, striking out six and walking one. The right-hander is 6-0 with a 2.55 ERA over his last 14 starts since May 28.

• LAST START: Aug. 14 vs. Houston, took a no-decision in Oakland’s 2-1 loss; 1 earned run on 8 hits in 8.1 innings; 6 strikeouts, 1 walk, 1 home run, 97 pitches, 66 for strikes.

• LAST VS. MARINERS: June 23, took a no-decision in Oakland’s 6-3 loss; 3 earned runs on 5 hits in 7.0 innings; 6 strikeouts, 1 walk, 2 home runs, 108 pitches, 71 for strikes.

• CAREER VS. MARINERS: 2-2, 5.10 ERA in 5 starts covering 30.0 innings; 27 strikeouts, 14 walks, 6 home runs, 1.20 WHIP.

• AT O.COM COLISEUM: 10-8, 3.34 ERA in 28 starts covering 178.0 innings; 122 strikeouts, 58 walks, 11 home runs, 1.20 WHIP.

• LOVE TO FACE: Dustin Ackley (0-for-9, .000), Michael Saunders (1-for-11, .091), Endy Chavez (1-for-6, .167), Michael Morse (1-for-6, .167).

• HATES TO FACE: Raul Ibanez (4-for-11, .364), Kendrys Morales (6-for-18, .333).

• CURRENT MARINERS VS. PARKER: 20-for-110, .182 BA, 26 strikeouts, 12 walks, 3 home runs, .262 on-base percentage.

MARINERS STATS / NOTES

• CURRENT ROAD TRIP: Three at Tampa Bay (Tuesday-Thursday), three at Texas (Friday-Sunday), three at Oakland (Monday-Wednesday). Following a day off Thursday, the Mariners will begin a six-game home stand Friday vs. the Angels and Rangers.
• Seattle’s 4-3 win Sunday was its eighth in the past 21 games.
• Kyle Seager extended his hitting streak to 14 games Sunday at Texas with a ninth-inning double that proved to be the winning run in Seattle’s 4-3 victory.
• Michael Saunders went 3-for-3 against Yu Darvish Sunday. Before that, Saunders had been 1-for-10 lifetime against Darvish.
• The Mariners gave struggling outfielder Michael Morse the day off Sunday. Morse is hitting .161 in 14 games since coming off the disabled list following a month-long leg-muscle issue. Endy Chavez took over in right field.
• Dustin Ackley is batting .338 (24×71) with four three-hit games since July 1.
• The five-run second inning endured by Felix Hernandez Saturday shot his ERA from 2.28 to 2.47, which ranks second in the American League.
• Oliver Perez had a 1.72 ERA in 38 appearances before the All-Star break. In 10 outings since, his ERA in 18.47 with 18 hits and 13 runs allowed in 6.2 innings.
• Franklin Gutierrez is batting .215 in 41 games during an extended rehab stint.

UPCOMING PROBABLES