By Christina Pazzanese, Globe Correspondent
It was a routine Saturday morning, except for the black ice on the road.
Gianfranco Esposito said he was driving his girlfriend, Patricia Sciacca, from Malden to Newton-Wellesley Hospital, where she works as a medical assistant, and they took their usual shortcut along Nonantum Road.
Noticing icy road conditions en route, Esposito had just remarked to Sciacca how dangerous the ice could be for drivers when he spotted something out of the corner of his eye: a sport utility vehicle that had flipped over and was partially submerged in the Charles River.
Esposito slowed down his Dodge pickup truck, and then turned around to get a better look.
‘‘He said, ‘Oh my God, there’s a car in the water,’’’ said Sciacca, 23, who hadn’t noticed anything.
‘‘She didn’t believe me,’’ said Esposito, 24.
Esposito and Sciacca remained deeply shaken this week as they recalled stumbling on the scene of a one-car crash in Newton on Saturday that killed Lauren Tsai, a 26-year-old graduate of the Massachusetts Institute of Technology who lived in Waltham. It was at least the third fatal accident since 2006 along the narrow four-lane parkway that stretches from Galen Street near Watertown Square to Soldiers Field Road in Brighton.
State Police said Tsai was driving her 2002 Nissan Pathfinder westbound when she lost control of the vehicle, which struck the curb and skidded down the embankment into the river. Tsai was pronounced dead of her injuries at the scene.
State Police believe the crash occurred several hours before she was found, said spokesman David Procopio, and the cause remained under investigation.
Tsai had been at a Celtics game with her brothers and father earlier that evening and had dropped off her younger brother at MIT before heading back home to Waltham, said Timothy Condon, whose fiancee was a close friend of Tsai.
Tsai earned a bachelor’s degree in mechanical engineering from MIT in 2004 and worked at Raytheon, according to an obituary posted Tuesday on the school’s website. She also played on the women’s basketball and field hockey teams. A brother, Michael Tsai, graduated from MIT in 2002 while another brother, Geoffrey Tsai is a senior there now, the site said.
A memorial service for Tsai is scheduled for Saturday from 6 p.m. to 8 p.m. at the Rand Wilson Funeral Home in Hanover, N.H. A funeral is to be held in the Rollins Chapel at Dartmouth College on Sunday at 10 a.m., the website said.
Esposito said that at the scene of the crash Saturday, he tossed his cellphone to Sciacca, told her to call 911, and then scrambled down the steep river bank. ‘‘I said, ‘Is anybody in there?’ I didn’t know if it just happened or if it had been there all night.’’
With the driver’s side door under water, Esposito waded into the river to try to open the passenger door. That’s when he peered into the car, darkened by the cold water, and saw Tsai’s body.
‘‘There’s someone in here!’’ he called out to Sciacca, who was by then, almost in tears. ‘‘It was just too much,’’ she said. ‘‘I didn’t want to see it.’’
Stunned and not sure what to do next, Esposito said he ran back up the embankment just as a state trooper pulled up to the scene. The men raced down to the car, uncertain how many people might be trapped inside. Though it appeared she had been driving, Esposito said Tsai was not strapped in by a seat belt. ‘‘We just reached in and pulled her right out,’’ he said.
The two men struggled to climb up the steep embankment made slippery by wet leaves and twigs. Once there, a jogger who happened upon the scene offered his assistance just as a second state trooper arrived and began performing CPR on Tsai. But Esposito said it seemed clear that it was too late.
Sciacca said the sight of the woman really hit home. ‘‘I knew it was someone our age,’’ she said. ‘‘I was really upset.’’
State Police said police and fire departments from Watertown and Newton, as well as Mass. Highway, assisted troopers at the scene. The road was closed for about an hour.
Nonantum Road has long been known as a treacherous, and often deadly, riverside speedway.
In February 2006, a Waltham couple were killed when their minivan spun off the road and hit a pole by Water Street.
In June that same year, a Waltham man was killed after his motorcycle struck a van at the intersection of Nonantum Road and Galen Street.