Nationals right fielder Jayson Werth leaps but cannot get to a ball in the Washington defeat. (Nick Wass/Associated Press)

For the four innings Taylor Jordan lasted Sunday afternoon, alarm overtook effectiveness. Jordan induced groundballs, cruised through the San Diego Padres’ punchless lineup and produced three zeroes. Still, his wan sinker lacked velocity and action, his ability to locate wavered and his head throbbed.

In the Washington Nationals4-2 loss to the Padres at Nationals Park, Jordan allowed one run over four innings as he pitched through a fever and a persistent headache that sapped his strength. Once Manager Matt Williams decided Jordan couldn’t continue through the illness, relievers Ross Detwiler and Aaron Barrett quickly turned a tie game into a defeat.

“I guess that they felt like I’d done enough,” Jordan said. “I don’t know. No one told me. I just got taken out.”

The Nationals issued six walks, including two by Barrett with the bases loaded. Padres right-hander Ian Kennedy dominated the Nationals’ lineup, which managed three hits against him in seven innings — and five total — while drawing zero walks and striking out nine times.

In the first game after left fielder Bryce Harper landed on the disabled list with a thumb sprain, primary replacement Nate McLouth socked his first home run as a National in the eighth inning. Jayson Werth’s leadoff single in the ninth allowed the tying run to come to the plate three times, but Adam LaRoche’s laser found Will Venable’s glove in deep right, and Padres closer Huston Street would not allow the Nationals (14-12) to produce their eighth comeback victory. They settled for a four-game series split, emblematic of a season neither rolling smoothly nor falling off track.

The root of their latest loss, which finalized their homestand record at 5-6, surfaced early Sunday morning. Jordan arrived at Nationals Park on almost no sleep, running a fever with a splitting headache. He felt chills and hot flashes. Nationals trainers administered an IV.

“There were some questions as to whether he would even start,” Williams said.

Jordan, a 25-year-old who made the Nationals with his strong spring training performance, entered Sunday with a 6.23 ERA, an 0-3 record and a fastball that lacked life compared with last season. Williams said afterward he plans on giving Jordan his next start, likely the last one he will make before Doug Fister returns from the disabled list.

Iin his weakened state Sunday, Jordan threw only one pitch at least 90 mph and pitched his sinker mostly between 85 and 87 mph. Along with speed, Jordan’s arsenal lacked action and power — the Padres did not swing and miss at any of his 63 pitches.

Still, Jordan managed desirable results. He escaped the first inning with a 6-4-3 double play, and the Padres kept hitting the ball on the ground. He navigated with more change-ups than usual, fooling the Padres into rolling over. Through three innings, he still pitched with a 1-0 lead.

“It wasn’t so bad out there,” Jordan said. “The headache just doesn’t go away. Other than that, I just wasn’t focused on much other than getting outs. It wasn’t like totally unbearable or anything.”

Jordan opened the fourth inning by walking Chris Denorfia, and four pitches later Yasmani Grandal drilled a change-up off the right wall. Grandal scored on a sacrifice fly, and Detwiler began warming up in the bullpen.

Jordan stranded two runners when Cameron Maybin popped out to foul ground next to first base to end the fourth. Williams determined Jordan’s diminished condition would not let him continue.

“He gave what he could give us today,” Williams said.

Once Williams rested Jordan, his bullpen frittered away the game. Detwiler surrendered a seemingly innocent two-out walk to Everth Cabrera with the bases empty. Cabrera swiped second base when Anthony Rendon couldn’t hold on to catcher Jose Lobaton’s throw. Cabrera scooted to third on Detwiler’s wild pitch, and he scored when Denorfia rolled a single back up the middle.

In 11 / 3 innings, Detwiler allowed four hits and a walk and absorbed three earned runs, the first he had allowed this season. Williams believes Detwiler fell victim to inconsistent work and said he plans to give Detwiler more, shorter appearances. Detwiler discounted that as a cause of his rough outing.

“I couldn’t throw a strike,” he said. “You have to make an adjustment. I didn’t. I pretty much cost us the game. I was just terrible today. It’s unacceptable.”

The Padres threatened again in the sixth, at which point the secondary benefit of Tanner Roark’s complete game Saturday surfaced. With a fully rested bullpen and Monday off, Williams could yank Detwiler and choose any reliever he wanted.

In from right field trotted Barrett. After Nick Hundley’s bloop single loaded the bases, Barrett struck out Kennedy. He needed one more out to escape the jam, but he lost control.

Cabrera had walked twice in 107 plate appearances, and Barrett walked him on four pitches. Rushing through his delivery, Barrett nearly hit Denorfia twice before he walked him, too, to force in another run and make it 4-1.

“There’s no excuse for it,” Barrett said. “I didn’t make pitches when I had to. We had an opportunity to tie the ballgame up. It could have been 2-2 there. I didn’t execute pitches and let the team down. That’s all I have for you, really.”

Left-hander Jerry Blevins provided a tourniquet with four consecutive outs, but the Nationals’ offense, resurgent over the weekend, never came to life against Kennedy. Rendon and Werth swatted consecutive doubles in the first inning to give the Nationals an immediate lead. Kennedy allowed one more hit the rest of the way.

“We just couldn’t get much going today,” McLouth said. “I thought Kennedy pitched a phenomenal game. We had him on the ropes a little bit during the first couple innings, but after that, he was lights out.”