Kansas guard Frank Mason III (0) drives against West Virginia guard Tarik Phillip (12) during the first half, Tuesday, Jan. 24, 2017 at WVU Coliseum.

The Kansas basketball team’s 18-game winning streak finally derailed Tuesday night, when the Jayhawks stumbled through the second half of a 85-69 loss at West Virginia.

The No. 18 Mountaineers (16-4 overall, 5-3 Big 12) handed the No. 2 Jayhawks (18-2, 7-1) their first conference loss of the season while defeating KU at WVU Coliseum, in Morgantown, West Virginia, for the fourth season in a row.

Freshman Josh Jackson tied his career high with 22 points to lead KU in scoring for the fifth time this season before fouling out late. Jackson went 4-for-4 from the 3-point line and 4-for-8 at the free-throw line.

Esa Ahmad scored 27 for West Virginia to lead all scorers, and the Mountaineers held KU to 42-percent shooting from the floor.

Here’s a quick look back at some of the action:

• The game turned when: The Mountaineers began finding easy baskets in the second half.

In the first half, KU only turned the ball over five times and knocked down 7 of 16 3-pointers (junior Devonte’ Graham and Jackson each buried two). Kansas led by as many as six and never trailed by more than four, as the visitors avoided disaster and cashed in when open looks presented themselves. Still, Kansas entered the locker room at halftime trailing, 38-35.

The more treacherous stretch for KU came in the opening minutes of the second half, with WVU converting via easy layups and a monster Ahmad dunk out of the gate, while the Jayhawks missed shots and turned the ball over, giving the home team a nine-point advantage — and its hungry crowd some energy — less than two minutes into the second half.

While Jackson and Frank Mason III (15 points, 6-for-16 shooting) kept KU in the mix in the second half, the Mountaineers began harnessing the juice provided by their fans and converting free throws, layups and dunks in the final six-plus minutes, while Kansas went through a stretch of nearly seven minutes late in the game with only two field goals to show for their troubles.

• Offensive highlight: West Virginia’s defensive energy didn’t sputter often, so the Jayhawks had to consider themselves fortunate when a basket came easily.

Late in the first half, with WVU on an 8-0 run and Kansas in serious need of calming basket, Graham (17 points) and Jackson made it happen when the Mountaineers had a lapse. Jackson cut behind the defense, along the baseline from the right corner.

Graham, whose 13-point first half put KU in sound position at intermission, surveyed the floor from up top and lofted an alley-oop look toward the rim for a simple and effective Jackson jam.

The superb freshman upped the ante in the second half on a fast break, though, when Jackson hammered home a one-handed slam after slicing between three WVU defenders.

• Defensive highlight: Looking to keep his primary two bigs, Landen Lucas and Carlton Bragg, from picking up too many fouls in the first half, Bill Self turned to freshman Mitch Lightfoot off the bench in the heat of what was a back-and-forth game in the first half.

A 6-foot-8 freshman from Gilbert, Arizona, Lightfoot didn’t look overwhelmed when his number was called. Just 20 seconds after checking in, he met Brandon Watkins at the rim and swatted away a layup try without committing a foul, doing exactly as Lucas would have in the same situation.

• Key stat: 3-point shooting. The Jayhawks couldn’t get high-percentage looks inside via post-ups or drives, so they pounced at the chance to take open 3-pointers when that’s what the defense allowed.

Kansas buried 13 of 29 (45 percent) on the Mountaineers’ home floor, and the defending Big 12 champs wouldn’t have had any sort of chance to win without knocking those down.

• Up next: The Jayhawks will face an even steeper road challenge Saturday, when they head to Rupp Arena to take on No. 4 Kentucky (5 p.m., ESPN).

— See what people were saying about the game during KUsports.com’s live coverage.

More news and notes from Kansas vs. West Virginia

• Unfamiliar territory: Jayhawks trounced against West Virginia, 85-69
• Tom Keegan: Jayhawks need Bragg to take step forward, just like WVU needed Ahmad
• Notebook: Mason receives star treatment, er booing, from WVU student section
• Keegan Ratings: Josh Jackson heats up from 3 and tops ratings in loss at West Virginia
• West Virginia ends KU’s winning streak