Heavy rain pours down as Stephen Strasburg delivers a pitch during the first inning at Nationals Park. (Jonathan Newton/The Washington Post)

Baseball guarantees bad days even for its greats, the afternoons when fastballs zip six inches too high, when rain makes the ball hard to grip, when popups fall to the turf and when, in some odd cases, even ointment becomes an enemy. Stephen Strasburg had a bad day Tuesday afternoon, the kind of day that reminds you the game sometimes makes even its most talented players miserable.

In the Washington Nationals6-1 loss to the San Diego Padres before 23,902 at Nationals Park, one of his worst days as a major leaguer, Strasburg lasted only four innings, including a disastrous first in which he allowed three runs and paused for eight minutes because of rain. He threw 81 pitches and yielded four runs on seven hits and two walks. He kicked dirt on the mound and glowered on his way off. His ERA rose from 1.64 to 2.25.

In his 25th career major league start, Strasburg allowed more than three earned runs for only the second time. Only one of his starts, when he pitched three innings last season in his second start back from Tommy John surgery, had been shorter than four innings.

“Sometimes it’s just not going to be your day and things aren’t going to go your way,” Strasburg said. “. . . It was just tough conditions all around. But I’m not one to make excuses.”

In an unusual postgame revelation, Manager Davey Johnson volunteered just how tough. Strasburg, Johnson said, had applied the analgesic ointment Hot Stuff to loosen up, and somehow, it had covered an area that would affect a pitcher’s performance.

“I can’t really tell you what the problem was, but some Hot Stuff got misplaced,” Johnson said. “It was on his shoulder and evidently — I don’t know how it got to where it got, but it was uncomfortable, to say the least.”

The sense in the Nationals’ clubhouse was that no one would have pulled a prank on Strasburg on the day he pitched, and that the ointment had found the wrong place by accident. Strasburg, who seemed miffed that Johnson had brought up the incident, didn’t address what had gone wrong.

“Yeah, you know, I’m going to keep that in the clubhouse,” Strasburg said.

Bryce Harper provided the Nationals’ lone bright spot in an otherwise bleak performance. In the fifth, Harper smashed a 1-0, 91-mph fastball from Padres starter Anthony Bass over the corner of the high wall in right-center field, following his first career home run Monday night with another that landed about 40 feet to the left. Harper became the first teenager to hit homers on consecutive days since Ken Griffey Jr. in 1989.

Bass otherwise silenced the Nationals, who had scored at least six runs in three of their past four games. They did not record their first hit until Ian Desmond led off the fourth with a single. Over eight innings, Bass allowed one run on five hits and one walk.

It was the kind of performance that has become expected of Strasburg. The weak-hitting opponent and the hazy sky seemed a perfect recipe for Strasburg, who had struck out 13 Pittsburgh Pirates in his last start. Rather than pitching a gem, Strasburg, with a crucial assist from his defense, unraveled at the start.

Leadoff hitter Will Venable popped up to shallow left-center field, high enough that the ball could have been caught by either left fielder Roger Bernadina or center fielder Rick Ankiel. They converged, looked at one another and treated the ball as if an infectious disease covered it. The ball plopped to the grass, and Venable wheeled into second with a double.

“I should have caught that ball,” Bernadina said.

Said Ankiel: “He thought I had it, and I thought he had it, and it dropped. It just [stinks]. As an outfield group, we never want to let that happen. But it happens. That’s baseball.”

After the inauspicious beginning, the inning never really improved. Strasburg allowed a one-out single. He walked two of the next five hitters, which, going back to his last start, gave him a highly uncharacteristic five walks out of nine hitters. Yonder Alonso gave the Padres a 1-0 lead with a single, and James Darnell’s walk loaded the bases.

Things went from bad to weird. The sunny sky opened up and poured rain as Strasburg pitched to John Baker. The count ran full before umpires halted the game. Strasburg had already thrown 33 pitches.

“I mean, the ball was absolutely drenched,” Strasburg said. “I probably could’ve hurt somebody.”

The grounds crew dragged out the tarp, but before they could spread it over the infield the rain stopped. They rolled it back up and off the field. After an eight-minute mini-delay, Strasburg took the mound again.

“It’s tough with them calling it when the count’s 3-2 with the bases loaded,” Strasburg said. “Obviously, you’ve got to throw a fastball over the plate.”

Baker smacked Strasburg’s 34th pitch of the inning back up the middle, a two-run single that put the Padres ahead, 3-0. Strasburg kicked dirt on the mound and slumped his shoulders, the kind of perturbed body language he typically avoids.

Strasburg would need five more pitches to finish the 39-pitch slog. Before Tuesday, he had allowed at least three earned runs in only four career starts. He paced slowly off the mound, eyes on the ground.

“It’s just tough because the ball was soaking wet up until the second-to-last hitter I faced that inning,” Strasburg said. “You’re just trying to guide it in there. And when they finally call it, it’s kind of like, okay, now I don’t have any margin for error.”

After nothing went right in the first, Strasburg issued no more walks and made only one more crucial mistake. In the third inning, Darnell blasted a 95-mph fastball deep to left field, about 10 rows shy of the concourse. Darnell became only the fourth right-handed batter to homer off Strasburg, and none had been more impressive.

“It’s just one of those games where you go out there and do your best to overcome the obstacles,” Strasburg said. “Sometimes you just can’t get out of it the way you want to. So I thought from the third inning, minus the home run, I pretty much settled down and started to locate the ball better.”

Strasburg ended his day by striking out Chase Headley with a change-up. After 81 pitches, he made one last slow trudge into the dugout, a very bad day behind him and a very odd explanation from his manager awaiting.