4:15 pm : The S&P 500 kicked off the fourth quarter on an upbeat note, climbing 0.8%. Stocks made the bulk of their advance during the opening 90 minutes before spending most of the afternoon near their highs. Late afternoon trade saw some profit-taking, but a final-minute surge sent the indices back to their highs as equities appeared unconcerned with the first day of the government shutdown.

All ten sectors posted gains as equities drew strength from typical start-of-quarter inflows. Risk assets also benefited from the rebound in Europe where yesterday's fears of a possible collapse of the Italian government were alleviated by reports indicating about 20 PDL ministers are ready to form a breakaway party supporting Prime Minister Enrico Letta. The fluid situation is expected to become a bit clearer tomorrow when the prime minister appears in front of the parliament.

The Nasdaq was the top performing index of the third quarter (+10.8%) and its relative strength continued into today's session. The index advanced 1.2% with support from its largest component. Apple (AAPL 487.96, +11.21) rose 2.4% after activist investor Carl Icahn said, in a tweet, that he pushed for a $150 billion buyback during his dinner meeting with Chief Executive Officer Tim Cook.

The outperformance of the Nasdaq was also due in part to the relative strength of the tech sector (+1.0%) and biotechnology. The iShares Nasdaq Biotechnology ETF (IBB 213.78, +4.18) climbed 2.0%, contributing to the strength of the health care sector (+1.3%), which ended in the lead.

In the health care space, Dow component Merck (MRK 48.74, +1.13) jumped 2.4% after announcing restructuring plans that include about 8,500 layoffs.

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