Manhattan’s median apartment price declined 2.8% to $655,000 in the third quarter, the first drop this year, as sales of lower-priced studio and one bedroom apartments increased.

The average price for apartments was pulled up 2.1% by a 15% surge in prices for three-bedroom apartments, according to property appraiser Miller Samuel Inc. and Douglas Elliman, the second-biggest Manhattan real estate brokerage. Buyers are paying $3.14 million on average for three-bedroom apartments.

Manhattan apartment prices are at records, rising to an average $1.07 million during the past quarter, as buyers took advantage of the lowest mortgage rates in six months. Studios and one bedroom apartments made up 54% of Manhattan sales at the end of September, up from 49% in June, Miller Samuel said.

“The lower rates open the market to a whole new segment of people,” said Pamela Liebman, 42, president and chief executive officer of Corcoran Group, the largest Manhattan brokerage. Manhattan has a population of about 1.5 million.

The average rate for a 30-year fixed mortgage fell half a percentage point to 5.7% in the third quarter, the lowest since early April, according to mortgage buyer Freddie Mac.

The cheapest apartment sold in the third quarter was $140,000 for a 265-square-foot studio, the equivalent of a 16- by 16-foot room, near the Empire State Building. The most-expensive apartment was a $21.2 million 10-room Midtown condo with 10,000 square feet of space and views of Central Park, Miller Samuel reported.

Luxury-apartment prices rose 8.5% in the third quarter to $4.11 million, exceeding the 3.8% increase of the prior quarter.

“We saw no slowdown in the third quarter, a time when typically our kind of buyers are in the south of France or the Hamptons,” said Donald Trump Jr., 26, vice president of development for the Trump Organization.

There were 19 sales at Trump Park Avenue, the former Delmonico Hotel, ranging from $800,000 for a 695-squarefoot apartment to $5 million for a 1,775-square-foot unit, Mr. Trump said. All the apartments have oak floors, kitchens with white marble countertops, and the building has a uniformed elevator attendant.

The average price for loft apartments, primarily in downtown Manhattan near Ground Zero, gained 0.8% to $1.48 million and the number of sales increased 35% to 236, according to Miller Samuel. The overall market had 2,337 sales.

The average price per square foot rose 4.2% to $820, an all-time high, as inventory, the number of properties on the market, fell 1.9% to 5,112.

“When you have increased demand and less supply, you’re going to see that square-foot number rise,” said Jonathan Miller, 44, president of Miller Samuel, in a telephone interview.

The surge of first-time buyers boosted the price of a two-bedroom apartment to $1.35 million from $1.34 million, Mr. Miller said.