(LEAD) (U20 World Cup) S. Korea should stay alert at all times vs. Portugal: coach
(ATTN: CHANGES photo; ADDS more comments in last 2 paras)By Joo Kyung-don
CHEONAN, South Korea, May 29 (Yonhap) -- South Korean football coach Shin Tae-yong said Monday his side will have to stay alert at all times when they play against Portugal in