An Example of Perseverance From A 64-Year-Old Woman.

Diana Nyad finally conquered the 110-mile passage from Cuba to Florida that had bedeviled her for 35 years.

Sharks steered clear, currents were friendly, and storms took most of the 2013 Labor Day weekend off.

The 64-year-old endurance swimmer emerged dazed and sunburned from the surf on Smathers Beach in Key West, FL, just before 2pm on Monday after nearly 53 hours in the ocean, a two-day, two-night swim from her starting point in Havana. She had survived the treacherous Florida Straits, a notorious stretch of water brimming with sharks, jellyfish, squalls and an unpredictable Gulf Stream. And she became the first person to do so unaided by the protection of a shark cage.

It was her fifth attempt, coming after four years of grueling training, precision planning and single-minded determination. Her face scorched and puffy from so many hours in the salt water, she leaned on one of her friends and said from the beach: “I have three messages. One is we should never, ever give up. Two is you never are too old to chase your dreams. Three is it looks like a solitary sport, but it’s a team.”

Coming at an age when few people try to set endurance records, Ms. Nyad’s swim lit up Twitter and Facebook with postings about perseverance and grit. Ms. Nyad’s success was built on her failures — the first in 1978, when she was 28, and the most recent last year at age 62. After each attempt, she improvised, learning what to adjust, whom to consult and which new protective protocol to consider.

“Diana did her homework,” said Bonnie Stoll, Ms. Nyad’s friend and chief handler, shortly after Ms. Nyad completed her swim.

Two summers ago, she was felled midswim by a long asthma attack, her first ever. This year, she added a pulmonologist to her 35-member support team, Ms. Stoll said.

Box jellyfish, which are especially venomous, have been a constant source of danger; Ms. Nyad was stung so badly on previous swims she had to stop. To break that cycle, she found an expert on box jellyfish this year to help her contain the threat.

In the evenings, Ms. Nyad donned a special suit with long sleeves and pant legs to protect her. She slathered “sting stopper” gel to form a barrier to keep out the venom. On Saturday night, she also wore a special mask that covered her face. But the mask proved uncomfortable, cutting her mouth and tongue so badly, and impeding her breathing, that she discarded it after the first night.

The course was mostly clear of box jellyfish this time. When she finally encountered a cluster, it was on her approach to Key West. The shark divers swam ahead of Ms. Nyad to disperse the swarm.

In 2011, Ms. Nyad decided to use a team of shark divers who carried special zappers to ward off the predators. Trial and error also presented new options. She learned which wet suits were more forgiving on her skin in saltwater and which special drinks and nutrition gels best fueled her. (She ingested them, sometimes through a tube, while treading water.)

But there were two things Ms. Nyad could not control: the weather and the current. This time, both cooperated.

“I think that Mother Nature said, ‘You know what? Let her go,’ ” Ms. Stoll said.

Unlike past swims derailed by squalls that pushed her off course, only one storm hit this weekend. It came on Sunday night and lasted a little under 90 minutes, Ms. Stoll said. Ms. Nyad followed her protocol and swam through it, accompanied by shark divers.

Sharks, always a menace, were nowhere to be seen this time.

The favorable currents carried her along so swiftly that Ms. Nyad finished her swim a day earlier than expected, Ms. Stoll said. On average, Ms. Nyad swims about 1.6 miles an hour. With the current propelling her, she cruised at 5 m.p.h. during one stretch, Ms. Stoll said, adding, “Everything was in our favor.”

Through the years, others have tried to swim from Cuba to Key West and failed. In June, an Australian, Chloe McCardel, swam 11 hours and 14 miles before jellyfish stings forced her to stop.

In 2012, another Australian, Penny Palfrey, swam 79 miles until strong currents waylaid her. In 1978, Walter Poenisch, an Ohio man, said he made the swim using flippers and a snorkel, but he lacked independent documentation to verify it.

Susie Maroney did complete the swim in 1997, but she did so inside a shark cage that was being pulled by a boat, providing a draft that made swimming much easier. The first time Ms. Nyad attempted the swim, in 1978, she also used a shark cage. She did not use a shark cage this time.

Whenever Ms. Nyad scrambled, heartbroken and exhausted, onto a boat after a failed attempt, she vowed it would be her last. “It was a fairy tale,” she said after her second attempt, in August 2011, “but the fairy tale didn’t come true.”

After last summer, Ms. Stoll said she was convinced that the Florida Straits were unswimmable. “I thought it wasn’t humanly possible or she would have done it,” Ms. Stoll said. “I was glad to be wrong.”