It dipped by 11 points at some stage but strong buying demand in the last hour of trading pulled it back to the starting price after gaining nearly 33 points in the last two sessions.
Trading on the Ho Chi Minh Stock Exchange fell by 17.9 percent to VND11.84 trillion ($509.40 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 13 tickers drop.
GVR of Vietnam Rubber Group fell 2.6 percent and BVH of insurance company Bao Viet Holdings dropped 2.3 percent.
Other losers included SAB of brewer Sabeco, PLX of fuel distributor Petrolimex and VRE of retail real estate arm Vincom Retail.
Twelve blue chips gained, with BID of state-owned lender BIDV rising 3.7 percent to the highest this month.
VNM of dairy giant Vinamilk gained 2.1 percent.
Other gainers included HPG of steelmaker Hoa Phat Group, GAS of state-owned Petrovietnam Gas and SSI of leading brokerage SSI Securities Corporation.
Foreign investors were net sellers to the tune of VND34.6 billion, mainly selling DPM of Petrovietnam Fertilizer & Chemicals Corporation and HPG of steelmaker Hoa Phat Group.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 0.54 percent while the UPCoM-Index at the Unlisted Public Companies Market fell 0.15 percent.