$Lyft Inc(LYFT.US)$ achieved a measure of profitability a quarter earlier than expected, marking a surprising comeback after the pandemic initially crushed demand for its ride-share service and later left it dealing with driver shortages.

Strong ride-hailing demand in the second quarter, combined with cost cuts throughout the pandemic, enabled Lyft on Tuesday to post its first profit on an adjusted basis before interest, taxes, depreciation and amortization. It's shares were slightly higher in after-hours trading.

Lyft President John Zimmer cautioned that it was tough to predict the future with the highly transmissible Delta variant boosting Covid-19 cases in the U.S., but said he was optimistic that the company wouldn't slip back from its profit milestone. Executives said Tuesday on a call with analysts that they expect the company to be profitable by the adjusted measure on a full-year basis in 2022.

Rival $UBER TECHNOLOGIES INC(UBER.US)$, which has a larger global footprint and a capital-intensive food-delivery business, expects to be profitable by the same measure by the fourth quarter. Uber and Lyft have yet to turn a net profit on the strength of their operations and haven't projected when they might. One-time gains have lifted both companies' fortunes; Uber posted a net profit in 2018 on the back of a roughly $5 billion gain from certain investments and divestitures.

Startups have long pointed to an adjusted metric to signal progress toward to future profits. These adjustments entail stripping out expenses such as asset write-downs that executives and many investors consider to be outside a company's fundamental operations.

On Tuesday, Lyft reported an adjusted Ebitda profit of $23.8 million for the three months ended June 30. That compares with the $44 million adjusted loss that analysts surveyed by FactSet were expecting. The company previously said it expected to reach the earnings milestone in the third quarter.

"People said we wouldn't survive the pandemic. People said we wouldn't be profitable. Lyft has defied the odds," Mr. Zimmer said in an interview. The health crisis, he said, "was disruptive and it was difficult, but these results validate the business model."

Uber's ride-hailing business that is more directly comparable with Lyft's operations has been profitable on the adjusted basis for years.

When the pandemic hit, "I was worried about all the businesses that we've invested in," said Lyft board member David Lawee, a partner at Alphabet Inc.'s venture-capital fund CapitalG. "It's stunning to see where Lyft is a year and a few months later," he said. "It shows that, even in extreme cases, they can balance swings in supply and demand, which bodes well for times that are more linear." The company's narrower focus on consumer transportation helped it turn things around quicker, Mr. Lawee said.

Lyft cut staff and shed money-losing businesses during the pandemic. In April, it sold its self-driving division to a Toyota Motor Corp. company -- a deal set to close in the third quarter. The company had moved up its profitability timetable to the third quarter from the fourth quarter as a result of the sale.

A better-than-expected recovery pushed the target ahead to the second quarter, Mr. Zimmer said.

Lyft's second-quarter revenue more than doubled to $765 million from $339 million in the year-earlier period, as its ridership inched closer to pre-pandemic levels. The company reported 17.1 million active riders in the quarter, up from 8.7 million a year earlier. Lyft had 22.9 million active riders at the end of 2019. Its second-quarter net loss narrowed to $251.9 million from $437 million a year-earlier.

Mr. Zimmer credited an enhanced mapping and dispatching technology for cutting wait time for riders, translating to repeat customers, and also for steering more business to drivers.

Beyond tracking the usual markers such as traffic, the company baked into its algorithm elements such as "what is the direction that drivers are driving on the street such that they have to make the least number of turns to get to you," Mr. Zimmer said. Lyft began fine-tuning its algorithm around the time the pandemic hit, so these tweaks drove results only after riders started returning earlier this year.

The company also reined in its sales and marketing expenses, phasing out discounts to riders during the pandemic. The company's average revenue per active rider increased to $44.63 in the second quarter from $39.06 in the same quarter a year earlier.

"It was a great quarter. There are no 'ifs,' 'ands' or 'buts' about it," said Ronald Josey, an analyst at JMP Securities. Analysts are watching to see if the company can control its sales and marketing costs in the future. Right now, "you don't have enough drivers and there's so much demand" that consumers don't need to be lured with deep discounts, Mr. Josey said.

Riders have returned quicker than drivers have, leading prices to skyrocket for Uber and Lyft rides in recent months.

In the latest quarter, Lyft topped the $39.77 revenue per active rider recorded for the second quarter of 2019, but marginally decreased from $45.13 in the preceding quarter this year when sales and marketing expenses stood at an all-time low as a percentage of revenue.

Both Uber and Lyft have spent on incentives and bonuses to encourage more drivers to take to the roads. Mr. Zimmer said 50% more drivers signed up to the platform in the second quarter compared with the first quarter, and that Lyft spent 24% less on driver incentives over the same period.

Driver earnings are at an-all time high as a result of the ongoing incentives. Mr. Zimmer said that Lyft drivers currently make more than $35 an hour in its busiest markets.

A near-term challenge is keeping drivers once the incentives disappear. Uber last week announced free online language classes for drivers, and Lyft previously said it was looking into a partnership to reduce one of driver's biggest expenses.