Oprah’s down in the basement, looking for her lost viewers.

“The Oprah Winfrey Show” hit an all-time ratings low for the week of June 28, averaging a 2.9 — the first time in the show’s 24-year history it fell below the 3.0 mark.

“Oprah” averaged 3.8 million viewers — good enough for eighth among all syndicated shows but almost 2 million viewers less than daytime’s reigning champ, “Judge Judy,” which has now beaten “Oprah” 14 out of the past 16 weeks.

“Oprah” was also down 15 percent from the previous week and was off 9 percent from the same week last year.

To be fair, it was the week leading into a holiday and “Oprah” has been in repeats since May — but so has nearly every other daytime show in the summer season. (“Judge Judy” was also in repeats that week.)

The week of June 28 also included preemptions for Wimbledon tennis on NBC stations. “Oprah,” which airs mostly on ABC stations, especially in the larger markets, was preempted in 14 markets.

“Oprah” is entering its 25th and final season.

“Although the ratings for our summer reruns have declined since last year, ‘The Oprah Winfrey Show’ continues to hold its place as the No. 1 daytime talk show for the last 24 years,” a spokesman said yesterday.