class Match{
    id:number;
    ...
    tournamentId:number;
    tournament: Tournament;
}

class Tournament{
    id:number;
    ...
    name:String;
}

get(): Observable<Match> {
    return Observable.create(obs => {
      tournamentService.get().pipe(toArray()).subscribe(tournaments => {//tournaments = [torunament1, tournament2]
        super.get().pipe(map(x => { let m = new Match(x); m.populateTournament(tournaments); obs.next(m); return m; })).subscribe(() => {
          obs.complete();
        });
      });
    });
  }