Ishchenko and Svetlana Romashina of Russia scored a leading 98.200 points in the duet technical routine on Sunday.
"They are machines," said Andrea Fuentes Fache of Spain. "I want to congratulate them because I don't understand how they can be so good."
Russia's opening 25 seconds of speedy legwork was perfectly timed to the rhythm of the Michael Jackson song "They Don't Care About Us." Ishchenko and Romashima executed the eight technical elements with precision, but the crowd cheered loudest for the duo's quickness and energy in the water.
"All the new routines we do other teams copy straight away, so we tried to keep our Olympics routine a secret," said Ishchenko, who trains 10 hours a day.
Ishchenko has won every technical solo event since the 2007 world championships.
"We have the best coaches and specialists in the world, and thank God, they still live in Russia," she said.
China's Huang Xuechen and Liu Ou were second at 96.100 after performing to kung fu music.
"We felt lots of pressure at the start because it is the first day of competition and these scores will contribute to the final score," Liu said.
Spain's Ona Carbonell Ballestero and Fuentes Fache took third at 96.000 with a flamenco-themed routine. They were slightly out of sync on their last thrust and 360-degree spin.
"We try not to count how long we are underwater because otherwise we would faint," Fuentes Fache said.
The Canadian pair of Marie-Pier Boudreau Gagnon and Elise Marcotte had the crowd clapping along with their routine to "Din Daa Daa" by George Krantz. They scored 94.500 to land in fourth.
The technical scores will be added to the marks from Monday's free routine, with the top 12 teams advancing to the final on Tuesday.
The U.S. duo of Mary Killman and Mariya Koroleva were 10th at 87.900 with a routine to the song "Think" by Aretha Franklin. Koroleva is of Russian heritage, so her loyalties are divided.
"It's difficult for me to live in America and just be an American because my heart is still Russian," she said. "It's difficult to divide between my love to America and my love to Russia, so I support both teams."
Killman and Koroleva put their personal stamp on their routine, coming up with some of the strokes, and designing the costumes that Killman's mother made. Still, they know they are chasing Russia, which has dominated the sport for several years. Russia swept all seven synchro titles at last year's world championships in Shanghai.
"The Russians are amazing," Killman said. "Even those who compete against them are in awe, let alone spectators who watch synchronized swimming. We're always trying to strive for Russia."