U.S. stocks turned mixed by mid-afternoon Thursday as a rally in Square (SQ )  shares boosted the tech sector, while a selloff in UnitedHealth (UNH) dragged on health care.

The S&P 500 fell 0.11%, the Dow Jones Industrial Average was flat, and the Nasdaq added 0.07%.

Mobile payments processing company Square opened for trading at $11.20, above its pricing of $9 a share. Shares were up 44%, trading at $12.96, by the afternoon. Square had previously set its IPO price range between $11 and $13 a share. The company, run by Twitter (TWTR) CEO Jack Dorsey, is one of the few private companies valued at $1 billion or more. The stock will begin trading on Thursday.

Other tech companies including Apple (AAPL) , Microsoft (MSFT) , Intel (INTC) , and Amazon (AMZN) joined the rally. The Technology SPDR ETF (XLK) added 0.6%.

UnitedHealth (UNH) fell more than 5% after issuing weak guidance and warning that it may exit its Obamacare plans. The health care insurer reduced its earnings forecasts in a sign that insurance plans through public exchanges had hit its profits. 

Pfizer (PFE)  was also dragging on health care following reports it is in talks to buy drugmaker Allergan (AGN) for as much as $370 to $380 a share, a deal that would total $150 billion and mark the healthcare industry's biggest deal ever. The two companies are in the final stages of merger talks, according to CNBC.

U.S. stocks shot above 1% on Wednesday after the central bank's meeting minutes upped the chances of a December rate hike and gave investors, and businesses, the ability to plan for the inevitable move. Most Fed members supported a rate hike next month, according to the minutes. However, members emphasized that no decision had been made and any move continued to be contingent on data.

The conditions for a rate hike have been met, Cleveland Fed President Loretta Mester told CNBC on Thursday. Mester said that the target of full employment has been achieved and that she is confident that the inflation target of 2% will be met soon. However, Mester did say that a December hike isn't a certainty; only that members felt that the "things were on track."

Separately, Atlanta Fed President Dennis Lockhart said in a speech that he was "comfortable" moving off of zero soon. Lockhart, a voting member of the Federal Open Market Committee, said that worries over low inflation were not enough to justify keeping rates at crises levels. 

Match (MTCH) , owner of dating sites OKCupid and Tinder, opened for trading Thursday around 12% higher than its IPO pricing at just above $13 a share. The company had priced its IPO at $12 a share, the low-end of its $12 to $14 range. The float will raise $400 million.

In earnings news, Best Buy (BBY - Get Report) shares slumped after disappointing quarterly sales and after it issued a gloomy holiday forecast. The electronics chain reported domestic same-store sales growth of 0.5%, far below estimates of 1.5% growth. The company expects a low-single digit percentage decline in revenue over the fourth quarter.

Keurig Green Mountain (GMCR - Get Report) shares spiked more than 20% after the coffeemaker company hiked its quarterly dividend to 32.5 cents a share. However, quarterly results disappointed expectations. Net income of 61 cents a share fell short of estimates of 70 cents, while revenue slid 13%.

Salesforce (CRM - Get Report) jumped 6% after far better-than-expected quarterly results. The cloud computing company earned an adjusted 21 cents a share, well above estimates of 4 cents a share, while revenue spiked 24% to $1.7 billion. Salesforce also raised its full-year 2016 sales guidance to $6.6 billion.

JM Smucker (SJM - Get Report) added 7% after earning $1.62 a share in its second quarter, 11 cents above estimates. The foods company reported a 40% jump in sales, driven by its acquisition of Big Heart Pet Brands earlier in the year.

Weekly jobless claims in the U.S. fell by 5,000 to 271,000, the Labor Department said Thursday, a sign of continuing tightening in the labor market. The average number of new claims for unemployment benefits rose by 3,000 to 270,750, an eight-week high but still at 15-year lows.

The Philadelphia Fed Index, a measure of business conditions in the region, showed improvement in November after two months of disappointing readings. The index rose to 1.9 over the month from negative 4.5 in October.