In the data center network, a packet-level load balancer such as random packet spraying (RPS) achieves high throughput by spraying data packets to all transmission paths, which easily suffers from the packet out-of-order problem under network asymmetry. While state-of-the-art network coding schemes can mitigate the issue, too many encoded redundant packets introduced by the network coding will cause extra traffic overhead, larger queueing delay and even TCP time out. In this paper, we propose OPportunistic Encoded Redundant (OPER), a middle-layer design upon existing coding schemes to mitigate the curse of redundant packets. Specifically, OPER uses opportunistic redundant packets which are replaceable by the data packets in the switches under heavy congestion. OPER is implemented as a shim layer between TCP and IP layers at end-hosts and a loadable plugin at switches, leaving existing TCP/IP protocols unmodified. The testbed and NS2 experiments show that, OPER reduces the average flow completion time by up to 71% compared with the state-of-the-art multipath coding schemes.