** S&P 500 .SPX snaps three-week winning streak, retreats 1.6% as jitters over stretched tech valuations, the economy curb risk appetite .N

** Dow .DJI falls 1.2%, while tech-heavy Nasdaq Composite .IXIC tumbles 3% for its worst week since early Apr

** U.S. 10-Year Treasury yield US10YT=RR ticks lower to end around 4.09%. Yields fell on Thurs on worries over a weakening U.S. labor market, along with uneasiness around the government shutdown and legality of President Trump's tariffs US/

** In the end, only a minority of sectors perturbed: Technology most agitated, while defensive plays exhibit composure

** Tech .SPLRCT tanks 4.2%. AI darling Palantir PLTR.O slides from peak after qtrly results surpass Wall Street's expectations; "Big Short" investor Michael Burry discloses bearish bets against PLTR and Nvidia NVDA.O

AI server maker Super Micro SMCI.O plummets 23% on week after qtrly miss on GPU delivery delays

Qualcomm QCOM.O falls despite upbeat qtrly forecast as potentially smaller Samsung 005930.KS business weighs

Semiconductor index .SOX sheds nearly 4%

** Consumer Discretionary .SPLRCD drops 1.5%. DoorDash DASH.O dives after Q3 profit miss on mounting costs, new investment plan unnerves investors

Tesla TSLA.O down; shareholders approve CEO Elon Musk's $1 trillion pay package

Though Amazon.com AMZN.O leaps on Mon after $38 bln AWS deal with OpenAI. AMZN ekes out fractional weekly gain

And McDonald's MCD.N rises slightly after Q3 global comp sales beat, aided by value meal offers

** Consumer Staples .SPLRCS up 0.8%. Tylenol-maker Kenvue KVUE.N jumps on nearly $49 bln buyout deal from Kleenex tissue maker Kimberly-Clark KMB.O, but KMB slumps

** Meanwhile, investor optimism wanes in latest week - AAII survey

** SPX performance YTD:

(Lance Tupper is a Reuters market analyst. The views expressed are his own)

((lance.tupper@tr.com))