R resolve multiple matches by selecting a random match

I am trying to merge two data.tables that result in multiple matches, to resolve this I want to select at random one of the multiple matches.

Say i have dt1 as such. Note, dt1 has 100+ columns but for demonstration purposes I've only written out three.

dt1 = data.table(x1 = c(100, 100, 200, 200, 200), 
                 x2 = c(101, 102, 201, 202, 203), 
                 v1 = c(1,2,3,4,5),
                 ...
                 vn = ...)

    x1  x2 v1
1: 100 101  1
2: 100 102  2
3: 200 201  3
4: 200 202  4
5: 200 203  5

Similarly dt2 looks like such. It also has more columns than what is shown below:

dt2 = data.table(x1 = c(100, 100, 100, 200, 200),
                 y1 = c(1, 2, 3, 4, 5),
                 ...)

    x1 y1
1: 100  1
2: 100  2
3: 100  3
4: 200  4
5: 200  5

What I want to do is merge on dt1 onto dt2 using column x1 to result in something like this:

    x1  x2 v1 y1
1: 100 101  1  1
2: 100 101  1  2
3: 100 102  2  3
4: 200 201  3  4
5: 200 203  5  5

This solution is very close to what I want Join data frames and select random row when there are multiple matches however, since both dt1 and dt2 has so many columns I cannot list out every single column (regardless of which way I want to merge dt1 to dt2 or dt2 to dt1).