As we close the books on 2013, one clear theme has emerged. Investors have flocked to developed economies and shunned emerging markets. The S&P 500 Index is on track for a nearly 30% gain this year, but many emerging markets have tumbled by double digits.

That kind of massive performance gap only emerges every decade or so, and for farsighted investors willing to look past near-term headwinds, emerging markets now represent tremendous relative value.

You don't need to tell that to the executives at major U.S. companies. They already know that emerging markets have generated -- and will continue to generate -- robust growth rates, thanks in large part to ever-rising middle classes. While developed economies are growing at a 2% pace, emerging-market economies are growing at a 4% to 5% pace. Asian emerging markets are rising an even more impressive 6%, according the International Monetary Fund (IMF).

The key takeaway: Even if you're wary of investing in volatile emerging markets directly, you can focus on the U.S. companies that are positioned to derive a rising level of sales and profits in these countries.

Thankfully, the strategists at Citigroup have already done the heavy lifting. In a recent report, Citi's Tobias Levkovich took a look at companies that already derive more than 20% of their revenue from emerging markets. These companies have invested millions of dollars to establish market dominance in these economies, and their first-mover advantage will reap rewards well into the future.

Which Industries Aren't Keeping Pace?
Levkovich has grouped these companies together in a portfolio he calls EMX, and not surprisingly, emerging-market exposure hasn't helped these stocks in 2013. The EMX basket has underperformed the S&P 500 by roughly 5 percentage points. Investors may be focusing on the fact that economic headwinds in 2013 are dampening the near-term financial performance for these companies.

The EMX portfolio holds a basket of 51 stocks, though I am most interested in the stocks that have notably underperformed the S&P 500 this year. Here are the EMX stocks that are up less than 10% in 2013.