Mystics coach Mike Thibault is frustrated by the team’s starts after halftime recently. (Jonathan Newton/The Washington Post)

Less than four minutes into the second half of the Washington Mystics’ most recent game Tuesday night, Coach Mike Thibault was so disappointed in his starters that he called a timeout to pull them off the Verizon Center court and insert his entire second unit.

The first five had allowed the Phoenix Mercury to score 10 consecutive points following the break, and just like that, Washington was on its way to a third consecutive loss, 81-66, amid another third-quarter swoon that had the winningest coach in WNBA history wondering aloud about lineup alterations to start future second halves.

Thibault will have had three days to explore that and other possible tweaks when the Mystics resume play Friday night against the Chicago Sky in the second game of a three-game homestand. Mired in a three-game slide, Washington (4-5) occupies fourth place in the Eastern Conference and sits below .500 for the first time since May 24.

“Part of it is we’ve had a couple different lineups that have started the third quarter,” Thibault said the day after reviewing film of the Mercury game. “But I don’t know that if it’s more the other team has upped it a notch after being ticked off that they’re tied or behind us. We had breakdowns at both ends, but they’re more mental things like missing someone that’s open or forcing a play that’s not there.”

The Mystics’ lowest scoring quarter of the season came last Friday night when they had nine points in the third quarter of a 64-61 loss to the Indiana Fever at Verizon Center. Less than 48 hours later, Washington either missed a field goal or committed a turnover on seven of its first eight possessions of the third quarter during an 81-64 loss to the Liberty at Madison Square Garden.

Phoenix Mercury center Brittney Griner battles Washington Mystics forward Tianna Hawkins for position under the boards on June 10. (Jonathan Newton/The Washington Post)

Compounding the issue has been balky shooting. Washington is second to last in field goal percentage (.406), and three starters are shooting below 40 percent. The Mystics are one of two teams shooting below 30 percent from three-point range, with the starting back court of Ivory Latta and Bria Hartley going 5 for 24 (21 percent) during this losing streak.

In its past three games, Washington also is averaging 15 turnovers. While that total is below a season average (16.6) that’s the second highest in the league, the timing of those wasted possessions has been problematic.

Against Phoenix, for instance, the Mystics had cut a deficit to 69-61 with 4 minutes 34 seconds left in regulation, but following an offensive rebound by Washington forward Emma Meesseman, Latta committed a turnover, and the Mercury expanded the lead to 12.

“I think sometimes when you go through these valleys of the season, you have to maintain your confidence level in your skills and your abilities and in what we’re trying to do as team,” Mystics guard Kara Lawson said. “Confident in that our scheme, our system does win.”

In Chicago (5-4), the Mystics draw an opponent that has dropped three straight and may be without 2013 rookie of the year Elena Delle Donne. The second leading scorer in the WNBA missed Tuesday’s 80-76 loss to the Seattle Storm because of a recurrence of Lyme Disease and is day-to-day.

Sky forward Jessica Breland also missed Tuesday’s game with a leg injury, as did center Sylvia Fowles, who is recovering from hip surgery and expected to be out until the end of this month.

“We have to become more aggressive because we’ve been too flat,” Mystics center Kia Vaughn said. “Not executing and not taking shots that we need to, and when I don’t take a shot or Ivory doesn’t take a shot or somebody else doesn’t take a shot, it leaves us with nothing. We just have to believe in ourselves.”