Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

The easiest, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. The Zacks Mutual Fund Rank, which covers over 19,000 mutual funds, has helped us identify three outstanding options that are perfect for any long-term investors' portfolios that is retirement-focused.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

Oppenheimer SteelPath MLP Alpha Y (MLPOX Quick QuoteMLPOX - Free Report) : 1.29% expense ratio and 1.1% management fee. MLPOX is a Sector - Energy fund, which are comprised of various changing and hugely important industries throughout the massive global energy sector. With annual returns of 10.42% over the last five years, this fund is a winner.

Fidelity Series Opportunistic Insights (FVWSX Quick QuoteFVWSX - Free Report) : 0.27% expense ratio and 0% management fee. FVWSX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. With yearly returns of 16.73% over the last five years, FVWSX is an effectively diversified fund with a long reputation of solidly positive performance.

MassMutual Premier Small/Mid Cap Opportunities A (DLBMX Quick QuoteDLBMX - Free Report) : 1.22% expense ratio and 0.58% management fee. DLBMX is a Small Cap Blend mutual fund, allowing investors a way to diversify their funds among various types of small-cap stocks. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 11.33% over the last five years.

These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.