The Cleveland company swung to a net loss of 2 cents a share from net income of 33 cents in the year-earlier period. Revenue tripled to $1.65 billion from $555.6 million.
Analysts surveyed by FactSet were expecting a net loss of 10 cents a share on revenue of $1.6 billion.
In the third quarter the company generated $150 million in free cash flow, derived from $246 million of cash from operations and $96 million in capital spending.
The company said that while its main market, the automotive industry, went through "unprecedented shutdowns" in the previous quarter, Cleveland-Cliffs prepared its inventories for when the industry bounced back.
Cleveland-Cliffs "quickly and efficiently [turned] things around," Chief Executive Lourenco Goncalves said in a statement.
"The new way of doing business we have been implementing in our newly acquired steel assets is demonstrated by our strong cost performance across the entire company."
In September, the company agreed to buy the U.S. operations of Luxembourg-based steel-and-mining company ArcelorMittal for $1.4 billion in cash and stock.
The transaction will make Cleveland-Cliffs the top flat-rolled-steel maker in North America, with combined shipments of about 17 million net tons in 2019. The deal would also make the company the largest producer of iron ore pellets.
At last check Cleveland-Cliffs shares were trading 5.8% higher at $8.75. On Friday they touched a 52-week high of $9.04. They've more than tripled off their 52-week low of $2.63, set in mid-March.