As Nyariki slowed, Julius Kibet, who won the event in 2004, sped up and passed his countryman to capture the race in 1 hour, 2 minutes, 2 seconds.
"Coming down [the stretch], I was sure I was going to win," said Nyariki, who took part in his first Philadelphia Distance Run. He finished second, 2 seconds behind Kibet.
"The confusion at the end cost me the race," Nyariki added.
More than 14,000 runners and walkers participated in the race, one of the largest half-marathons in the nation. Nyariki and Kibet, 25, were part of a small group of runners who led the field for the majority of the race, which starts and ends at Eakins Oval on the Parkway.
Nyariki was only 2 seconds off the lead and 1 second behind Kibet coming down Kelly Drive at the 10-mile mark. He held a slim advantage as the runners entered Eakins Oval, before Kibet cut inside him - on his right side - to pull ahead.
"Nyariki is very fast, and I know that he is very strong [around] the finish line," Kibet said. "So I worked very hard to see if I could stay with him."
Kibet and Nyariki were two of eight Kenyans who finished in the top 10 of the men's race.
Navajo runner Brandon Leslie, who trains in New Mexico, completed the race in 1:05:01, the fastest time among male U.S. Olympic trial qualifiers. Christopher Nirschel, 23, finished 43d and ran the fastest time for a Philadelphia man at 1:08:48.
Kenyan Pamela Chepchumba, 28, finished first among the women with a time of 1:08:45.
Claire Duncan, a graduate of Friends' Central High School and the University of Pennsylvania, finished 18th and ran the fastest time for a Philadelphia woman, completing the race in 1:18:46.
Several runners have competed in every Philadelphia Distance Run since 1978.
Mike Geiger of Medford is one of more than 25 30-year runners who participated in this year's event. Geiger, 60, dedicates every race to his daughter, Amanda, who was killed along with three of her friends by a drunken driver in 1999. She was 17.
Since 2005, Kaitlyn Willard's father, Joseph, has run behind her for the last few miles of the race while her mother watches from the finish line.
Kaitlyn Willard, a 17-year-old Upper Darby High senior who is paralyzed below the knees, earned the fastest time for a wheelchair participant for the third consecutive year. She finished the event in 1:25:58.
"I love this race," she said. "I look forward to [it] every year."
Julius Kibet, Kenya, 1:02:02
Tom Nyariki, Kenya, 1:02:04
John Yuda, Tanzania, 1:02:05
MacDonald Ondara, Kenya, 1:02:10
Festus Langat, Kenya, 1:02:28
Charles Munyeki, Kenya, 1:02:28
Samuel Ndereba, Kenya, 1:02:37
Linuis Maiyo, Kenya, 1:02:46
Demesse Tefera, Ethiopia, 1:02:46
Daniel Kipkoech, Kenya, 1:02:59
Karim ElMabchour, Ethiopia, 1:03:11
Pius Muli, Kenya, 1:03:12
Nicholas Kamayka, Kenya, 1:03:20
John Itati, Kenya, 1:03:25
Girma Tola, Ethiopia, 1:03:51
Joseph Koech, Kenya, 1:04:08
Gurmessa Mergessa, Ethiopia, 1:04:35
Reuben Chebii, Kenya, 1:04:39
Macharia Yuot, San Ysidro, CA, 1:04:42
Gilbert Koech, Kenya, 1:04:48
Pamela Chepchumba, Kenya, 1:08:45
Alice Timbilili, Kenya, 1:08:56
Edna Kiplagat, Kenya, 1:10:11
Sharon Cherop, Kenya, 1:10:21
Hiromi Ominami, Japan, 1:10:41
Ashu Kasim, Ethiopia, 1:11:19
Angelina Mutuku, Kenya, 1:11:20
Olga Kravtsova, Belaruss, 1:11:33
Nuta Olaru, Romania, 1:11:46
Aziza Aliyu, Ethiopia, 1:12:45
Alemstsehay Msignnaw, Ethiopia, 1:12:48
Caroline Chepkorir, Kenya, 1:13:07
Akemi Ozaki, Japan, 1:13:12
Melisa Christian, United States, 1:14:38
Takami Ominami, Japan, 1:16:08
Kara Roy, United States, 1:16:56
Laura Turner, Washington D.C., 1:17:44
Claire Duncan, Philadelphia, 1:18:46
Paige Miller, State College, Pa., 1:18:54
Abby Dean, Philadelphia, 1:19:07