CAIRO — Islamists claimed a decisive victory on Wednesday as early election results put them on track to win a dominant majority in Egypt’s first Parliament since the ouster of Hosni Mubarak, the most significant step yet in the religious movement’s rise since the start of the Arab Spring.

The party formed by the Muslim Brotherhood, Egypt’s mainstream Islamist group, appeared to have taken about 40 percent of the vote, as expected. But a big surprise was the strong showing of ultraconservative Islamists, called Salafis, many of whom see most popular entertainment as sinful and reject women’s participation in voting or public life.

Analysts in the state-run news media said early returns indicated that Salafi groups could take as much as a quarter of the vote, giving the two groups of Islamists combined control of nearly 65 percent of the parliamentary seats.

That victory came at the expense of the liberal parties and youth activists who set off the revolution, affirming their fears that they would be unable to compete with Islamists who emerged from the Mubarak years organized and with an established following. Poorly organized and internally divided, the liberal parties could not compete with Islamists disciplined by decades as the sole opposition to Mr. Mubarak. “We were washed out,” said Shady el-Ghazaly Harb, one of the most politically active of the group.