If I were you, I would ring the travel agent and get them to cut out the unnecessary northward backtrack to OPO.
There are only 3 weekly OPO-LAD flights at present, whereas from LIS there is a daily flight on TAP and 2 daily flights (except for Wednesdays) on TAAG.
If you miss your flight at OPO, they will likely have to fly you back down to LIS anyway to get you to LAD. Crazy routing.