Ulitmate Goal:
Create a map of lists (contactIdsToOpportunities)  which maps a contact id to the list of opportunities that contact is associated with within the OpportunityContactRole object - all based on a limited # of contact id's, only opportunities within the last 30 days.

As I'm trying to access the subquery field values to build my map of lists, its generating the following error: 
Invalid aggregate relationship OpportunityContactRole for Opportunity

I'm trying to use this approach:  http://www.infallibletechie.com/2012/04/how-to-get-subquery-field-value-using.html

I'm grateful for any help, so thanks in advance!
-Bronco

CODE:
set <Id> evtsContactIds = new set <Id>{'0035000000yim1c’,’0035000000cin2f’};//insert contacts id's here
map <Id, List <Opportunity>> contactIdsToOpportunities = new Map <Id, List <Opportunity>>();

for (Opportunity o: [SELECT Id, CloseDate, Description, Name, (SELECT ContactId FROM OpportunityContactRoles WHERE ContactId IN: evtsContactIds) FROM Opportunity WHERE CloseDate >= LAST_N_DAYS: 30 AND Id IN(SELECT OpportunityId FROM OpportunityContactRole WHERE ContactId IN: evtsContactIds) ORDER BY CloseDate DESC])
{
    List < OpportunityContactRole > opptys = new List < OpportunityContactRole > ();
    opptys = o.getSObjects('OpportunityContactRole'); //very rarely used method, but this gets the records from the subquery, 
    Id oppContId;
    for (OpportunityContactRole opt: opptys)
    {
        oppContId = opt.ContactId;

        if (contactIdsToOpportunities.containsKey(oppContId))
        {
            List < Opportunity > contactsOpportunities = contactIdsToOpportunities.get(oppContId);
            if (contactsOpportunities.size() <= 3) //this is what determines that the code will only return the latest 3 opportunities
            {
                contactsOpportunities.add(o);
                contactIdsToOpportunities.put(oppContId, contactsOpportunities);
            }
        }
        else
        {
            contactIdsToOpportunities.put(oppContId, new List <Opportunity>{o});
        }
    }
}