Wahab had 68,612 votes (56.5%) to Hernandez's 52,755 (43.4%) with 52.52% of the expected vote counted, according to KQED's 2:25 a.m. update. ABC7 showed the same totals. Neither had reported an AP call.
The seat opened in April when Rep. Eric Swalwell resigned. Wahab, a former state senator, beat Hernandez in a contentious August special election to finish the term, and the two Democrats met again in November for a full two-year term.
The district covers Fremont, Hayward and the Tri-Valley.
A win would give Wahab her first full term after only a few months in Congress.
All results are unofficial election-night and early-morning counts as of Wednesday, Nov. 4. Counties keep counting mail and provisional ballots for days, and certification comes later, so margins can shift, especially in close contests.