Audiences at the Goodman Theatre press opening of “Pamplona” witnessed a heightened level of drama Tuesday as star Stacy Keach fell ill and director Robert Falls suspended the performance of the one-man show about two thirds of the way through its 80 minute running time.

In the initial scenes it seemed as though Keach’s portrayal of late-life Ernest Hemingway was meant to be more than a study of writer’s block and something closer to the onset of dementia. As the fabled writer struggled to complete a Life magazine story about bullfighters he mentioned the many concussions he had suffered in past years, while also taking pills and drinking whiskey. And at first the repetition of lines seemed to be suggesting Hemingway’s distracted     mind. But increasingly it became clear that this was not the script as written by Jim McGrath, and that Keach was trying to hold on until he got hold of the play again.

About an hour into the action, Keach was interrupted by a P.A. announcement by the stage manager that the show was stopping due to technical difficulties. This allowed the actor to exit the stage with dignity, and Falls soon came out to announce the cancellation of the show and to explain that the actor had been ill all day but had been determined to go on despite his condition.

Speaking to me by phone a short while later, Falls said the show was an “absolute aberration” from Keach’s robust work in 10 preview performances that began May 19.

At those earlier shows, Falls said, “he was flawless from the word go, and had nothing but great success and brilliant performances.”

Falls said Keach had seemed shaky and dehydrated during a run-through earlier Tuesday but resisted Falls’ suggestions that he rest or see a doctor. “He’s such a pro,” the director said.

Falls confirmed that the repeated lines were Keach’s attempt to re-orient himself and not part of the script. Keach’s wife and daughter were present for the opening and brought the actor home after he left the stage.

McGrath’s “Pamplona” is set in a hotel room in that northern Spanish city that is the site of the annual “running of the bulls.” And the story Hemingway is trying to write is about about the rivalry between two famous matadors. Along the way he recalls many aspects of his own life.

Observing events at the Goodman on Tuesday served as a vivid reminder of the focus, discipline and physical and mental energy required for live performance, especially a one-person show.

Over the years I have seen a few dancers suffer injuries on stage. And very recently, during a Chicago Symphony Orchestra concert, a musician who felt faint very discreetly moved to an exit door at the back of the stage, slowly collapsed, and was quietly lifted backstage without a single missed note as the rest of the orchestra played on under Maestro Muti’s direction.

Keach used every weapon in his considerable arsenal to keep the play going. It was a master class in endurance. And his director came to the rescue in a most graceful way.

“Men like Hemingway don’t exist anymore,” Keach, 75, told me earlier this month. “My grandfather was like him; so was the director John Huston. They just experienced life in a different way. The reason Hemingway loved bullfighting so much was the life-and-death experience of it, and you can hear it in the beautiful passages he wrote in ‘Death in the Afternoon’ and ‘The Sun Also Rises,’ some of which are in the play.”

Keach stayed in the ring like a champion matador on Tuesday night.

One final note: I took a friend who works with the Spanish Tourist Office in Chicago to the performance and she told me that the hotel room set by Kevin Depinet was ideal (aside from one large bed replacing twin beds). She had visited “the Hemingway room” (which can be booked at a significant price) at the Gran Hotel La Perla, where, from his balcony, the famous writer had access to a perfect view of the running of the bulls along Estafeta Street.